diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 13ba4e3ce..cf519b475 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -36,8 +36,7 @@ repos:
   - id: black
     # By default, this ignores pyi files, though black supports them
     types: [text]
-    # Not all Python files are Blacked, yet
-    files: ^(setup.py|pybind11|tests/extra|tools).*\.pyi?$
+    files: \.pyi?$
 
 # Changes tabs to spaces
 - repo: https://github.com/Lucas-C/pre-commit-hooks
diff --git a/docs/benchmark.py b/docs/benchmark.py
index 023477212..33d78fb4e 100644
--- a/docs/benchmark.py
+++ b/docs/benchmark.py
@@ -14,7 +14,7 @@ def generate_dummy_code_pybind11(nclasses=10):
 
     for cl in range(nclasses):
         decl += "class cl%03i;\n" % cl
-    decl += '\n'
+    decl += "\n"
 
     for cl in range(nclasses):
         decl += "class cl%03i {\n" % cl
@@ -22,18 +22,17 @@ def generate_dummy_code_pybind11(nclasses=10):
         bindings += '    py::class_<cl%03i>(m, "cl%03i")\n' % (cl, cl)
         for fn in range(nfns):
             ret = random.randint(0, nclasses - 1)
-            params  = [random.randint(0, nclasses - 1) for i in range(nargs)]
+            params = [random.randint(0, nclasses - 1) for i in range(nargs)]
             decl += "    cl%03i *fn_%03i(" % (ret, fn)
             decl += ", ".join("cl%03i *" % p for p in params)
             decl += ");\n"
-            bindings += '        .def("fn_%03i", &cl%03i::fn_%03i)\n' % \
-                (fn, cl, fn)
+            bindings += '        .def("fn_%03i", &cl%03i::fn_%03i)\n' % (fn, cl, fn)
         decl += "};\n\n"
-        bindings += '        ;\n'
+        bindings += "        ;\n"
 
     result = "#include <pybind11/pybind11.h>\n\n"
     result += "namespace py = pybind11;\n\n"
-    result += decl + '\n'
+    result += decl + "\n"
     result += "PYBIND11_MODULE(example, m) {\n"
     result += bindings
     result += "}"
@@ -46,7 +45,7 @@ def generate_dummy_code_boost(nclasses=10):
 
     for cl in range(nclasses):
         decl += "class cl%03i;\n" % cl
-    decl += '\n'
+    decl += "\n"
 
     for cl in range(nclasses):
         decl += "class cl%03i {\n" % cl
@@ -54,18 +53,20 @@ def generate_dummy_code_boost(nclasses=10):
         bindings += '    py::class_<cl%03i>("cl%03i")\n' % (cl, cl)
         for fn in range(nfns):
             ret = random.randint(0, nclasses - 1)
-            params  = [random.randint(0, nclasses - 1) for i in range(nargs)]
+            params = [random.randint(0, nclasses - 1) for i in range(nargs)]
             decl += "    cl%03i *fn_%03i(" % (ret, fn)
             decl += ", ".join("cl%03i *" % p for p in params)
             decl += ");\n"
-            bindings += '        .def("fn_%03i", &cl%03i::fn_%03i, py::return_value_policy<py::manage_new_object>())\n' % \
-                (fn, cl, fn)
+            bindings += (
+                '        .def("fn_%03i", &cl%03i::fn_%03i, py::return_value_policy<py::manage_new_object>())\n'
+                % (fn, cl, fn)
+            )
         decl += "};\n\n"
-        bindings += '        ;\n'
+        bindings += "        ;\n"
 
     result = "#include <boost/python.hpp>\n\n"
     result += "namespace py = boost::python;\n\n"
-    result += decl + '\n'
+    result += decl + "\n"
     result += "BOOST_PYTHON_MODULE(example) {\n"
     result += bindings
     result += "}"
@@ -73,17 +74,19 @@ def generate_dummy_code_boost(nclasses=10):
 
 
 for codegen in [generate_dummy_code_pybind11, generate_dummy_code_boost]:
-    print ("{")
+    print("{")
     for i in range(0, 10):
         nclasses = 2 ** i
         with open("test.cpp", "w") as f:
             f.write(codegen(nclasses))
         n1 = dt.datetime.now()
-        os.system("g++ -Os -shared -rdynamic -undefined dynamic_lookup "
+        os.system(
+            "g++ -Os -shared -rdynamic -undefined dynamic_lookup "
             "-fvisibility=hidden -std=c++14 test.cpp -I include "
-            "-I /System/Library/Frameworks/Python.framework/Headers -o test.so")
+            "-I /System/Library/Frameworks/Python.framework/Headers -o test.so"
+        )
         n2 = dt.datetime.now()
         elapsed = (n2 - n1).total_seconds()
-        size = os.stat('test.so').st_size
+        size = os.stat("test.so").st_size
         print("   {%i, %f, %i}," % (nclasses * nfns, elapsed, size))
-    print ("}")
+    print("}")
diff --git a/docs/conf.py b/docs/conf.py
index 831cf6f58..dca362e2f 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -21,40 +21,44 @@ import subprocess
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
 # documentation root, use os.path.abspath to make it absolute, like shown here.
-#sys.path.insert(0, os.path.abspath('.'))
+# sys.path.insert(0, os.path.abspath('.'))
 
 # -- General configuration ------------------------------------------------
 
 # If your documentation needs a minimal Sphinx version, state it here.
-#needs_sphinx = '1.0'
+# needs_sphinx = '1.0'
 
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
-extensions = ['breathe', 'sphinxcontrib.rsvgconverter', 'sphinxcontrib.moderncmakedomain']
+extensions = [
+    "breathe",
+    "sphinxcontrib.rsvgconverter",
+    "sphinxcontrib.moderncmakedomain",
+]
 
-breathe_projects = {'pybind11': '.build/doxygenxml/'}
-breathe_default_project = 'pybind11'
-breathe_domain_by_extension = {'h': 'cpp'}
+breathe_projects = {"pybind11": ".build/doxygenxml/"}
+breathe_default_project = "pybind11"
+breathe_domain_by_extension = {"h": "cpp"}
 
 # Add any paths that contain templates here, relative to this directory.
-templates_path = ['.templates']
+templates_path = [".templates"]
 
 # The suffix(es) of source filenames.
 # You can specify multiple suffix as a list of string:
 # source_suffix = ['.rst', '.md']
-source_suffix = '.rst'
+source_suffix = ".rst"
 
 # The encoding of source files.
-#source_encoding = 'utf-8-sig'
+# source_encoding = 'utf-8-sig'
 
 # The master toctree document.
-master_doc = 'index'
+master_doc = "index"
 
 # General information about the project.
-project = 'pybind11'
-copyright = '2017, Wenzel Jakob'
-author = 'Wenzel Jakob'
+project = "pybind11"
+copyright = "2017, Wenzel Jakob"
+author = "Wenzel Jakob"
 
 # The version info for the project you're documenting, acts as replacement for
 # |version| and |release|, also used in various other places throughout the
@@ -78,37 +82,37 @@ language = None
 
 # There are two options for replacing |today|: either, you set today to some
 # non-false value, then it is used:
-#today = ''
+# today = ''
 # Else, today_fmt is used as the format for a strftime call.
-#today_fmt = '%B %d, %Y'
+# today_fmt = '%B %d, %Y'
 
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.
-exclude_patterns = ['.build', 'release.rst']
+exclude_patterns = [".build", "release.rst"]
 
 # The reST default role (used for this markup: `text`) to use for all
 # documents.
-default_role = 'any'
+default_role = "any"
 
 # If true, '()' will be appended to :func: etc. cross-reference text.
-#add_function_parentheses = True
+# add_function_parentheses = True
 
 # If true, the current module name will be prepended to all description
 # unit titles (such as .. function::).
-#add_module_names = True
+# add_module_names = True
 
 # If true, sectionauthor and moduleauthor directives will be shown in the
 # output. They are ignored by default.
-#show_authors = False
+# show_authors = False
 
 # The name of the Pygments (syntax highlighting) style to use.
-#pygments_style = 'monokai'
+# pygments_style = 'monokai'
 
 # A list of ignored prefixes for module index sorting.
-#modindex_common_prefix = []
+# modindex_common_prefix = []
 
 # If true, keep warnings as "system message" paragraphs in the built documents.
-#keep_warnings = False
+# keep_warnings = False
 
 # If true, `todo` and `todoList` produce output, else they produce nothing.
 todo_include_todos = False
@@ -119,144 +123,137 @@ todo_include_todos = False
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
 
-on_rtd = os.environ.get('READTHEDOCS', None) == 'True'
+on_rtd = os.environ.get("READTHEDOCS", None) == "True"
 
 if not on_rtd:  # only import and set the theme if we're building docs locally
     import sphinx_rtd_theme
-    html_theme = 'sphinx_rtd_theme'
+
+    html_theme = "sphinx_rtd_theme"
     html_theme_path = [sphinx_rtd_theme.get_html_theme_path()]
 
-    html_context = {
-        'css_files': [
-            '_static/theme_overrides.css'
-        ]
-    }
+    html_context = {"css_files": ["_static/theme_overrides.css"]}
 else:
     html_context = {
-        'css_files': [
-            '//media.readthedocs.org/css/sphinx_rtd_theme.css',
-            '//media.readthedocs.org/css/readthedocs-doc-embed.css',
-            '_static/theme_overrides.css'
+        "css_files": [
+            "//media.readthedocs.org/css/sphinx_rtd_theme.css",
+            "//media.readthedocs.org/css/readthedocs-doc-embed.css",
+            "_static/theme_overrides.css",
         ]
     }
 
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the
 # documentation.
-#html_theme_options = {}
+# html_theme_options = {}
 
 # Add any paths that contain custom themes here, relative to this directory.
-#html_theme_path = []
+# html_theme_path = []
 
 # The name for this set of Sphinx documents.  If None, it defaults to
 # "<project> v<version> documentation".
-#html_title = None
+# html_title = None
 
 # A shorter title for the navigation bar.  Default is the same as html_title.
-#html_short_title = None
+# html_short_title = None
 
 # The name of an image file (relative to this directory) to place at the top
 # of the sidebar.
-#html_logo = None
+# html_logo = None
 
 # The name of an image file (within the static path) to use as favicon of the
 # docs.  This file should be a Windows icon file (.ico) being 16x16 or 32x32
 # pixels large.
-#html_favicon = None
+# html_favicon = None
 
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,
 # so a file named "default.css" will overwrite the builtin "default.css".
-html_static_path = ['_static']
+html_static_path = ["_static"]
 
 # Add any extra paths that contain custom files (such as robots.txt or
 # .htaccess) here, relative to this directory. These files are copied
 # directly to the root of the documentation.
-#html_extra_path = []
+# html_extra_path = []
 
 # If not '', a 'Last updated on:' timestamp is inserted at every page bottom,
 # using the given strftime format.
-#html_last_updated_fmt = '%b %d, %Y'
+# html_last_updated_fmt = '%b %d, %Y'
 
 # If true, SmartyPants will be used to convert quotes and dashes to
 # typographically correct entities.
-#html_use_smartypants = True
+# html_use_smartypants = True
 
 # Custom sidebar templates, maps document names to template names.
-#html_sidebars = {}
+# html_sidebars = {}
 
 # Additional templates that should be rendered to pages, maps page names to
 # template names.
-#html_additional_pages = {}
+# html_additional_pages = {}
 
 # If false, no module index is generated.
-#html_domain_indices = True
+# html_domain_indices = True
 
 # If false, no index is generated.
-#html_use_index = True
+# html_use_index = True
 
 # If true, the index is split into individual pages for each letter.
-#html_split_index = False
+# html_split_index = False
 
 # If true, links to the reST sources are added to the pages.
-#html_show_sourcelink = True
+# html_show_sourcelink = True
 
 # If true, "Created using Sphinx" is shown in the HTML footer. Default is True.
-#html_show_sphinx = True
+# html_show_sphinx = True
 
 # If true, "(C) Copyright ..." is shown in the HTML footer. Default is True.
-#html_show_copyright = True
+# html_show_copyright = True
 
 # If true, an OpenSearch description file will be output, and all pages will
 # contain a <link> tag referring to it.  The value of this option must be the
 # base URL from which the finished HTML is served.
-#html_use_opensearch = ''
+# html_use_opensearch = ''
 
 # This is the file name suffix for HTML files (e.g. ".xhtml").
-#html_file_suffix = None
+# html_file_suffix = None
 
 # Language to be used for generating the HTML full-text search index.
 # Sphinx supports the following languages:
 #   'da', 'de', 'en', 'es', 'fi', 'fr', 'h', 'it', 'ja'
 #   'nl', 'no', 'pt', 'ro', 'r', 'sv', 'tr'
-#html_search_language = 'en'
+# html_search_language = 'en'
 
 # A dictionary with options for the search language support, empty by default.
 # Now only 'ja' uses this config value
-#html_search_options = {'type': 'default'}
+# html_search_options = {'type': 'default'}
 
 # The name of a javascript file (relative to the configuration directory) that
 # implements a search results scorer. If empty, the default will be used.
-#html_search_scorer = 'scorer.js'
+# html_search_scorer = 'scorer.js'
 
 # Output file base name for HTML help builder.
-htmlhelp_basename = 'pybind11doc'
+htmlhelp_basename = "pybind11doc"
 
 # -- Options for LaTeX output ---------------------------------------------
 
 latex_elements = {
-# The paper size ('letterpaper' or 'a4paper').
-#'papersize': 'letterpaper',
-
-# The font size ('10pt', '11pt' or '12pt').
-#'pointsize': '10pt',
-
-# Additional stuff for the LaTeX preamble.
-'preamble': r'''
+    # The paper size ('letterpaper' or 'a4paper').
+    # 'papersize': 'letterpaper',
+    # The font size ('10pt', '11pt' or '12pt').
+    # 'pointsize': '10pt',
+    # Additional stuff for the LaTeX preamble.
+    "preamble": r"""
 \DeclareUnicodeCharacter{00A0}{}
 \DeclareUnicodeCharacter{2194}{<->}
-''',
-
-# Latex figure (float) alignment
-#'figure_align': 'htbp',
+""",
+    # Latex figure (float) alignment
+    # 'figure_align': 'htbp',
 }
 
 # Grouping the document tree into LaTeX files. List of tuples
 # (source start file, target name, title,
 #  author, documentclass [howto, manual, or own class]).
 latex_documents = [
-  (master_doc, 'pybind11.tex', 'pybind11 Documentation',
-   'Wenzel Jakob', 'manual'),
+    (master_doc, "pybind11.tex", "pybind11 Documentation", "Wenzel Jakob", "manual"),
 ]
 
 # The name of an image file (relative to this directory) to place at the top of
@@ -265,32 +262,29 @@ latex_documents = [
 
 # For "manual" documents, if this is true, then toplevel headings are parts,
 # not chapters.
-#latex_use_parts = False
+# latex_use_parts = False
 
 # If true, show page references after internal links.
-#latex_show_pagerefs = False
+# latex_show_pagerefs = False
 
 # If true, show URL addresses after external links.
-#latex_show_urls = False
+# latex_show_urls = False
 
 # Documents to append as an appendix to all manuals.
-#latex_appendices = []
+# latex_appendices = []
 
 # If false, no module index is generated.
-#latex_domain_indices = True
+# latex_domain_indices = True
 
 
 # -- Options for manual page output ---------------------------------------
 
 # One entry per manual page. List of tuples
 # (source start file, name, description, authors, manual section).
-man_pages = [
-    (master_doc, 'pybind11', 'pybind11 Documentation',
-     [author], 1)
-]
+man_pages = [(master_doc, "pybind11", "pybind11 Documentation", [author], 1)]
 
 # If true, show URL addresses after external links.
-#man_show_urls = False
+# man_show_urls = False
 
 
 # -- Options for Texinfo output -------------------------------------------
@@ -299,35 +293,41 @@ man_pages = [
 # (source start file, target name, title, author,
 #  dir menu entry, description, category)
 texinfo_documents = [
-  (master_doc, 'pybind11', 'pybind11 Documentation',
-   author, 'pybind11', 'One line description of project.',
-   'Miscellaneous'),
+    (
+        master_doc,
+        "pybind11",
+        "pybind11 Documentation",
+        author,
+        "pybind11",
+        "One line description of project.",
+        "Miscellaneous",
+    ),
 ]
 
 # Documents to append as an appendix to all manuals.
-#texinfo_appendices = []
+# texinfo_appendices = []
 
 # If false, no module index is generated.
-#texinfo_domain_indices = True
+# texinfo_domain_indices = True
 
 # How to display URL addresses: 'footnote', 'no', or 'inline'.
-#texinfo_show_urls = 'footnote'
+# texinfo_show_urls = 'footnote'
 
 # If true, do not generate a @detailmenu in the "Top" node's menu.
-#texinfo_no_detailmenu = False
+# texinfo_no_detailmenu = False
 
-primary_domain = 'cpp'
-highlight_language = 'cpp'
+primary_domain = "cpp"
+highlight_language = "cpp"
 
 
 def generate_doxygen_xml(app):
-    build_dir = os.path.join(app.confdir, '.build')
+    build_dir = os.path.join(app.confdir, ".build")
     if not os.path.exists(build_dir):
         os.mkdir(build_dir)
 
     try:
-        subprocess.call(['doxygen', '--version'])
-        retcode = subprocess.call(['doxygen'], cwd=app.confdir)
+        subprocess.call(["doxygen", "--version"])
+        retcode = subprocess.call(["doxygen"], cwd=app.confdir)
         if retcode < 0:
             sys.stderr.write("doxygen error code: {}\n".format(-retcode))
     except OSError as e:
diff --git a/tests/conftest.py b/tests/conftest.py
index a2350d041..362eb8069 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -18,9 +18,9 @@ import env
 # Early diagnostic for failed imports
 import pybind11_tests  # noqa: F401
 
-_unicode_marker = re.compile(r'u(\'[^\']*\')')
-_long_marker = re.compile(r'([0-9])L')
-_hexadecimal = re.compile(r'0x[0-9a-fA-F]+')
+_unicode_marker = re.compile(r"u(\'[^\']*\')")
+_long_marker = re.compile(r"([0-9])L")
+_hexadecimal = re.compile(r"0x[0-9a-fA-F]+")
 
 # Avoid collecting Python3 only files
 collect_ignore = []
@@ -30,7 +30,7 @@ if env.PY2:
 
 def _strip_and_dedent(s):
     """For triple-quote strings"""
-    return textwrap.dedent(s.lstrip('\n').rstrip())
+    return textwrap.dedent(s.lstrip("\n").rstrip())
 
 
 def _split_and_sort(s):
@@ -40,11 +40,14 @@ def _split_and_sort(s):
 
 def _make_explanation(a, b):
     """Explanation for a failed assert -- the a and b arguments are List[str]"""
-    return ["--- actual / +++ expected"] + [line.strip('\n') for line in difflib.ndiff(a, b)]
+    return ["--- actual / +++ expected"] + [
+        line.strip("\n") for line in difflib.ndiff(a, b)
+    ]
 
 
 class Output(object):
     """Basic output post-processing and comparison"""
+
     def __init__(self, string):
         self.string = string
         self.explanation = []
@@ -54,7 +57,11 @@ class Output(object):
 
     def __eq__(self, other):
         # Ignore constructor/destructor output which is prefixed with "###"
-        a = [line for line in self.string.strip().splitlines() if not line.startswith("###")]
+        a = [
+            line
+            for line in self.string.strip().splitlines()
+            if not line.startswith("###")
+        ]
         b = _strip_and_dedent(other).splitlines()
         if a == b:
             return True
@@ -65,6 +72,7 @@ class Output(object):
 
 class Unordered(Output):
     """Custom comparison for output without strict line ordering"""
+
     def __eq__(self, other):
         a = _split_and_sort(self.string)
         b = _split_and_sort(other)
@@ -175,7 +183,7 @@ def msg():
 # noinspection PyUnusedLocal
 def pytest_assertrepr_compare(op, left, right):
     """Hook to insert custom failure explanation"""
-    if hasattr(left, 'explanation'):
+    if hasattr(left, "explanation"):
         return left.explanation
 
 
@@ -189,8 +197,8 @@ def suppress(exception):
 
 
 def gc_collect():
-    ''' Run the garbage collector twice (needed when running
-    reference counting tests with PyPy) '''
+    """Run the garbage collector twice (needed when running
+    reference counting tests with PyPy)"""
     gc.collect()
     gc.collect()
 
diff --git a/tests/test_buffers.py b/tests/test_buffers.py
index d6ca0776b..f0f370844 100644
--- a/tests/test_buffers.py
+++ b/tests/test_buffers.py
@@ -46,8 +46,8 @@ def test_to_python():
     mat[3, 2] = 7.0
     assert mat[2, 3] == 4
     assert mat[3, 2] == 7
-    assert struct.unpack_from('f', mat, (3 * 4 + 2) * 4) == (7, )
-    assert struct.unpack_from('f', mat, (2 * 4 + 3) * 4) == (4, )
+    assert struct.unpack_from("f", mat, (3 * 4 + 2) * 4) == (7,)
+    assert struct.unpack_from("f", mat, (2 * 4 + 3) * 4) == (4,)
 
     mat2 = np.array(mat, copy=False)
     assert mat2.shape == (5, 4)
@@ -83,31 +83,31 @@ def test_pointer_to_member_fn():
     for cls in [m.Buffer, m.ConstBuffer, m.DerivedBuffer]:
         buf = cls()
         buf.value = 0x12345678
-        value = struct.unpack('i', bytearray(buf))[0]
+        value = struct.unpack("i", bytearray(buf))[0]
         assert value == 0x12345678
 
 
 def test_readonly_buffer():
     buf = m.BufferReadOnly(0x64)
     view = memoryview(buf)
-    assert view[0] == b'd' if env.PY2 else 0x64
+    assert view[0] == b"d" if env.PY2 else 0x64
     assert view.readonly
 
 
 def test_selective_readonly_buffer():
     buf = m.BufferReadOnlySelect()
 
-    memoryview(buf)[0] = b'd' if env.PY2 else 0x64
+    memoryview(buf)[0] = b"d" if env.PY2 else 0x64
     assert buf.value == 0x64
 
-    io.BytesIO(b'A').readinto(buf)
-    assert buf.value == ord(b'A')
+    io.BytesIO(b"A").readinto(buf)
+    assert buf.value == ord(b"A")
 
     buf.readonly = True
     with pytest.raises(TypeError):
-        memoryview(buf)[0] = b'\0' if env.PY2 else 0
+        memoryview(buf)[0] = b"\0" if env.PY2 else 0
     with pytest.raises(TypeError):
-        io.BytesIO(b'1').readinto(buf)
+        io.BytesIO(b"1").readinto(buf)
 
 
 def test_ctypes_array_1d():
diff --git a/tests/test_builtin_casters.py b/tests/test_builtin_casters.py
index 08d38bc15..bd7996b62 100644
--- a/tests/test_builtin_casters.py
+++ b/tests/test_builtin_casters.py
@@ -37,79 +37,85 @@ def test_unicode_conversion():
         with pytest.raises(UnicodeDecodeError):
             m.bad_utf8_u8string()
 
-    assert m.u8_Z() == 'Z'
-    assert m.u8_eacute() == u'é'
-    assert m.u16_ibang() == u'‽'
-    assert m.u32_mathbfA() == u'𝐀'
-    assert m.wchar_heart() == u'♥'
+    assert m.u8_Z() == "Z"
+    assert m.u8_eacute() == u"é"
+    assert m.u16_ibang() == u"‽"
+    assert m.u32_mathbfA() == u"𝐀"
+    assert m.wchar_heart() == u"♥"
     if hasattr(m, "has_u8string"):
-        assert m.u8_char8_Z() == 'Z'
+        assert m.u8_char8_Z() == "Z"
 
 
 def test_single_char_arguments():
     """Tests failures for passing invalid inputs to char-accepting functions"""
+
     def toobig_message(r):
         return "Character code point not in range({0:#x})".format(r)
+
     toolong_message = "Expected a character, but multi-character string found"
 
-    assert m.ord_char(u'a') == 0x61  # simple ASCII
-    assert m.ord_char_lv(u'b') == 0x62
-    assert m.ord_char(u'é') == 0xE9  # requires 2 bytes in utf-8, but can be stuffed in a char
+    assert m.ord_char(u"a") == 0x61  # simple ASCII
+    assert m.ord_char_lv(u"b") == 0x62
+    assert (
+        m.ord_char(u"é") == 0xE9
+    )  # requires 2 bytes in utf-8, but can be stuffed in a char
     with pytest.raises(ValueError) as excinfo:
-        assert m.ord_char(u'Ā') == 0x100  # requires 2 bytes, doesn't fit in a char
+        assert m.ord_char(u"Ā") == 0x100  # requires 2 bytes, doesn't fit in a char
     assert str(excinfo.value) == toobig_message(0x100)
     with pytest.raises(ValueError) as excinfo:
-        assert m.ord_char(u'ab')
+        assert m.ord_char(u"ab")
     assert str(excinfo.value) == toolong_message
 
-    assert m.ord_char16(u'a') == 0x61
-    assert m.ord_char16(u'é') == 0xE9
-    assert m.ord_char16_lv(u'ê') == 0xEA
-    assert m.ord_char16(u'Ā') == 0x100
-    assert m.ord_char16(u'‽') == 0x203d
-    assert m.ord_char16(u'♥') == 0x2665
-    assert m.ord_char16_lv(u'♡') == 0x2661
+    assert m.ord_char16(u"a") == 0x61
+    assert m.ord_char16(u"é") == 0xE9
+    assert m.ord_char16_lv(u"ê") == 0xEA
+    assert m.ord_char16(u"Ā") == 0x100
+    assert m.ord_char16(u"‽") == 0x203D
+    assert m.ord_char16(u"♥") == 0x2665
+    assert m.ord_char16_lv(u"♡") == 0x2661
     with pytest.raises(ValueError) as excinfo:
-        assert m.ord_char16(u'🎂') == 0x1F382  # requires surrogate pair
+        assert m.ord_char16(u"🎂") == 0x1F382  # requires surrogate pair
     assert str(excinfo.value) == toobig_message(0x10000)
     with pytest.raises(ValueError) as excinfo:
-        assert m.ord_char16(u'aa')
+        assert m.ord_char16(u"aa")
     assert str(excinfo.value) == toolong_message
 
-    assert m.ord_char32(u'a') == 0x61
-    assert m.ord_char32(u'é') == 0xE9
-    assert m.ord_char32(u'Ā') == 0x100
-    assert m.ord_char32(u'‽') == 0x203d
-    assert m.ord_char32(u'♥') == 0x2665
-    assert m.ord_char32(u'🎂') == 0x1F382
+    assert m.ord_char32(u"a") == 0x61
+    assert m.ord_char32(u"é") == 0xE9
+    assert m.ord_char32(u"Ā") == 0x100
+    assert m.ord_char32(u"‽") == 0x203D
+    assert m.ord_char32(u"♥") == 0x2665
+    assert m.ord_char32(u"🎂") == 0x1F382
     with pytest.raises(ValueError) as excinfo:
-        assert m.ord_char32(u'aa')
+        assert m.ord_char32(u"aa")
     assert str(excinfo.value) == toolong_message
 
-    assert m.ord_wchar(u'a') == 0x61
-    assert m.ord_wchar(u'é') == 0xE9
-    assert m.ord_wchar(u'Ā') == 0x100
-    assert m.ord_wchar(u'‽') == 0x203d
-    assert m.ord_wchar(u'♥') == 0x2665
+    assert m.ord_wchar(u"a") == 0x61
+    assert m.ord_wchar(u"é") == 0xE9
+    assert m.ord_wchar(u"Ā") == 0x100
+    assert m.ord_wchar(u"‽") == 0x203D
+    assert m.ord_wchar(u"♥") == 0x2665
     if m.wchar_size == 2:
         with pytest.raises(ValueError) as excinfo:
-            assert m.ord_wchar(u'🎂') == 0x1F382  # requires surrogate pair
+            assert m.ord_wchar(u"🎂") == 0x1F382  # requires surrogate pair
         assert str(excinfo.value) == toobig_message(0x10000)
     else:
-        assert m.ord_wchar(u'🎂') == 0x1F382
+        assert m.ord_wchar(u"🎂") == 0x1F382
     with pytest.raises(ValueError) as excinfo:
-        assert m.ord_wchar(u'aa')
+        assert m.ord_wchar(u"aa")
     assert str(excinfo.value) == toolong_message
 
     if hasattr(m, "has_u8string"):
-        assert m.ord_char8(u'a') == 0x61  # simple ASCII
-        assert m.ord_char8_lv(u'b') == 0x62
-        assert m.ord_char8(u'é') == 0xE9  # requires 2 bytes in utf-8, but can be stuffed in a char
+        assert m.ord_char8(u"a") == 0x61  # simple ASCII
+        assert m.ord_char8_lv(u"b") == 0x62
+        assert (
+            m.ord_char8(u"é") == 0xE9
+        )  # requires 2 bytes in utf-8, but can be stuffed in a char
         with pytest.raises(ValueError) as excinfo:
-            assert m.ord_char8(u'Ā') == 0x100  # requires 2 bytes, doesn't fit in a char
+            assert m.ord_char8(u"Ā") == 0x100  # requires 2 bytes, doesn't fit in a char
         assert str(excinfo.value) == toobig_message(0x100)
         with pytest.raises(ValueError) as excinfo:
-            assert m.ord_char8(u'ab')
+            assert m.ord_char8(u"ab")
         assert str(excinfo.value) == toolong_message
 
 
@@ -129,19 +135,19 @@ def test_bytes_to_string():
     assert m.strlen(to_bytes("a\x00b")) == 1  # C-string limitation
 
     # passing in a utf8 encoded string should work
-    assert m.string_length(u'💩'.encode("utf8")) == 4
+    assert m.string_length(u"💩".encode("utf8")) == 4
 
 
 @pytest.mark.skipif(not hasattr(m, "has_string_view"), reason="no <string_view>")
 def test_string_view(capture):
     """Tests support for C++17 string_view arguments and return values"""
     assert m.string_view_chars("Hi") == [72, 105]
-    assert m.string_view_chars("Hi 🎂") == [72, 105, 32, 0xf0, 0x9f, 0x8e, 0x82]
-    assert m.string_view16_chars(u"Hi 🎂") == [72, 105, 32, 0xd83c, 0xdf82]
+    assert m.string_view_chars("Hi 🎂") == [72, 105, 32, 0xF0, 0x9F, 0x8E, 0x82]
+    assert m.string_view16_chars(u"Hi 🎂") == [72, 105, 32, 0xD83C, 0xDF82]
     assert m.string_view32_chars(u"Hi 🎂") == [72, 105, 32, 127874]
     if hasattr(m, "has_u8string"):
         assert m.string_view8_chars("Hi") == [72, 105]
-        assert m.string_view8_chars(u"Hi 🎂") == [72, 105, 32, 0xf0, 0x9f, 0x8e, 0x82]
+        assert m.string_view8_chars(u"Hi 🎂") == [72, 105, 32, 0xF0, 0x9F, 0x8E, 0x82]
 
     assert m.string_view_return() == u"utf8 secret 🎂"
     assert m.string_view16_return() == u"utf16 secret 🎂"
@@ -154,40 +160,52 @@ def test_string_view(capture):
         m.string_view_print("utf8 🎂")
         m.string_view16_print(u"utf16 🎂")
         m.string_view32_print(u"utf32 🎂")
-    assert capture == u"""
+    assert (
+        capture
+        == u"""
         Hi 2
         utf8 🎂 9
         utf16 🎂 8
         utf32 🎂 7
     """
+    )
     if hasattr(m, "has_u8string"):
         with capture:
             m.string_view8_print("Hi")
             m.string_view8_print(u"utf8 🎂")
-        assert capture == u"""
+        assert (
+            capture
+            == u"""
             Hi 2
             utf8 🎂 9
         """
+        )
 
     with capture:
         m.string_view_print("Hi, ascii")
         m.string_view_print("Hi, utf8 🎂")
         m.string_view16_print(u"Hi, utf16 🎂")
         m.string_view32_print(u"Hi, utf32 🎂")
-    assert capture == u"""
+    assert (
+        capture
+        == u"""
         Hi, ascii 9
         Hi, utf8 🎂 13
         Hi, utf16 🎂 12
         Hi, utf32 🎂 11
     """
+    )
     if hasattr(m, "has_u8string"):
         with capture:
             m.string_view8_print("Hi, ascii")
             m.string_view8_print(u"Hi, utf8 🎂")
-        assert capture == u"""
+        assert (
+            capture
+            == u"""
             Hi, ascii 9
             Hi, utf8 🎂 13
         """
+        )
 
 
 def test_integer_casting():
@@ -199,8 +217,14 @@ def test_integer_casting():
     if env.PY2:
         assert m.i32_str(long(-1)) == "-1"  # noqa: F821 undefined name 'long'
         assert m.i64_str(long(-1)) == "-1"  # noqa: F821 undefined name 'long'
-        assert m.i64_str(long(-999999999999)) == "-999999999999"  # noqa: F821 undefined name
-        assert m.u64_str(long(999999999999)) == "999999999999"  # noqa: F821 undefined name 'long'
+        assert (
+            m.i64_str(long(-999999999999))  # noqa: F821 undefined name 'long'
+            == "-999999999999"
+        )
+        assert (
+            m.u64_str(long(999999999999))  # noqa: F821 undefined name 'long'
+            == "999999999999"
+        )
     else:
         assert m.i64_str(-999999999999) == "-999999999999"
         assert m.u64_str(999999999999) == "999999999999"
@@ -236,16 +260,22 @@ def test_tuple(doc):
     assert m.tuple_passthrough([True, "test", 5]) == (5, "test", True)
     assert m.empty_tuple() == ()
 
-    assert doc(m.pair_passthrough) == """
+    assert (
+        doc(m.pair_passthrough)
+        == """
         pair_passthrough(arg0: Tuple[bool, str]) -> Tuple[str, bool]
 
         Return a pair in reversed order
     """
-    assert doc(m.tuple_passthrough) == """
+    )
+    assert (
+        doc(m.tuple_passthrough)
+        == """
         tuple_passthrough(arg0: Tuple[bool, str, int]) -> Tuple[int, str, bool]
 
         Return a triple in reversed order
     """
+    )
 
     assert m.rvalue_pair() == ("rvalue", "rvalue")
     assert m.lvalue_pair() == ("lvalue", "lvalue")
@@ -372,7 +402,7 @@ def test_numpy_bool():
     assert convert(np.bool_(False)) is False
     assert noconvert(np.bool_(True)) is True
     assert noconvert(np.bool_(False)) is False
-    cant_convert(np.zeros(2, dtype='int'))
+    cant_convert(np.zeros(2, dtype="int"))
 
 
 def test_int_long():
@@ -382,7 +412,8 @@ def test_int_long():
     long."""
 
     import sys
-    must_be_long = type(getattr(sys, 'maxint', 1) + 1)
+
+    must_be_long = type(getattr(sys, "maxint", 1) + 1)
     assert isinstance(m.int_cast(), int)
     assert isinstance(m.long_cast(), int)
     assert isinstance(m.longlong_cast(), must_be_long)
diff --git a/tests/test_call_policies.py b/tests/test_call_policies.py
index ec005c132..e0413d145 100644
--- a/tests/test_call_policies.py
+++ b/tests/test_call_policies.py
@@ -16,10 +16,13 @@ def test_keep_alive_argument(capture):
     with capture:
         p.addChild(m.Child())
         assert ConstructorStats.detail_reg_inst() == n_inst + 1
-    assert capture == """
+    assert (
+        capture
+        == """
         Allocating child.
         Releasing child.
     """
+    )
     with capture:
         del p
         assert ConstructorStats.detail_reg_inst() == n_inst
@@ -35,10 +38,13 @@ def test_keep_alive_argument(capture):
     with capture:
         del p
         assert ConstructorStats.detail_reg_inst() == n_inst
-    assert capture == """
+    assert (
+        capture
+        == """
         Releasing parent.
         Releasing child.
     """
+    )
 
 
 def test_keep_alive_return_value(capture):
@@ -49,10 +55,13 @@ def test_keep_alive_return_value(capture):
     with capture:
         p.returnChild()
         assert ConstructorStats.detail_reg_inst() == n_inst + 1
-    assert capture == """
+    assert (
+        capture
+        == """
         Allocating child.
         Releasing child.
     """
+    )
     with capture:
         del p
         assert ConstructorStats.detail_reg_inst() == n_inst
@@ -68,10 +77,13 @@ def test_keep_alive_return_value(capture):
     with capture:
         del p
         assert ConstructorStats.detail_reg_inst() == n_inst
-    assert capture == """
+    assert (
+        capture
+        == """
         Releasing parent.
         Releasing child.
     """
+    )
 
 
 # https://foss.heptapod.net/pypy/pypy/-/issues/2447
@@ -82,14 +94,17 @@ def test_alive_gc(capture):
     p.addChildKeepAlive(m.Child())
     assert ConstructorStats.detail_reg_inst() == n_inst + 2
     lst = [p]
-    lst.append(lst)   # creates a circular reference
+    lst.append(lst)  # creates a circular reference
     with capture:
         del p, lst
         assert ConstructorStats.detail_reg_inst() == n_inst
-    assert capture == """
+    assert (
+        capture
+        == """
         Releasing parent.
         Releasing child.
     """
+    )
 
 
 def test_alive_gc_derived(capture):
@@ -101,14 +116,17 @@ def test_alive_gc_derived(capture):
     p.addChildKeepAlive(m.Child())
     assert ConstructorStats.detail_reg_inst() == n_inst + 2
     lst = [p]
-    lst.append(lst)   # creates a circular reference
+    lst.append(lst)  # creates a circular reference
     with capture:
         del p, lst
         assert ConstructorStats.detail_reg_inst() == n_inst
-    assert capture == """
+    assert (
+        capture
+        == """
         Releasing parent.
         Releasing child.
     """
+    )
 
 
 def test_alive_gc_multi_derived(capture):
@@ -123,15 +141,18 @@ def test_alive_gc_multi_derived(capture):
     # +3 rather than +2 because Derived corresponds to two registered instances
     assert ConstructorStats.detail_reg_inst() == n_inst + 3
     lst = [p]
-    lst.append(lst)   # creates a circular reference
+    lst.append(lst)  # creates a circular reference
     with capture:
         del p, lst
         assert ConstructorStats.detail_reg_inst() == n_inst
-    assert capture == """
+    assert (
+        capture
+        == """
         Releasing parent.
         Releasing child.
         Releasing child.
     """
+    )
 
 
 def test_return_none(capture):
@@ -167,17 +188,23 @@ def test_keep_alive_constructor(capture):
     with capture:
         p = m.Parent(m.Child())
         assert ConstructorStats.detail_reg_inst() == n_inst + 2
-    assert capture == """
+    assert (
+        capture
+        == """
         Allocating child.
         Allocating parent.
     """
+    )
     with capture:
         del p
         assert ConstructorStats.detail_reg_inst() == n_inst
-    assert capture == """
+    assert (
+        capture
+        == """
         Releasing parent.
         Releasing child.
     """
+    )
 
 
 def test_call_guard():
diff --git a/tests/test_callbacks.py b/tests/test_callbacks.py
index d5d0e045d..039b877ce 100644
--- a/tests/test_callbacks.py
+++ b/tests/test_callbacks.py
@@ -42,17 +42,19 @@ def test_bound_method_callback():
 
 
 def test_keyword_args_and_generalized_unpacking():
-
     def f(*args, **kwargs):
         return args, kwargs
 
     assert m.test_tuple_unpacking(f) == (("positional", 1, 2, 3, 4, 5, 6), {})
-    assert m.test_dict_unpacking(f) == (("positional", 1), {"key": "value", "a": 1, "b": 2})
+    assert m.test_dict_unpacking(f) == (
+        ("positional", 1),
+        {"key": "value", "a": 1, "b": 2},
+    )
     assert m.test_keyword_args(f) == ((), {"x": 10, "y": 20})
     assert m.test_unpacking_and_keywords1(f) == ((1, 2), {"c": 3, "d": 4})
     assert m.test_unpacking_and_keywords2(f) == (
         ("positional", 1, 2, 3, 4, 5),
-        {"key": "value", "a": 1, "b": 2, "c": 3, "d": 4, "e": 5}
+        {"key": "value", "a": 1, "b": 2, "c": 3, "d": 4, "e": 5},
     )
 
     with pytest.raises(TypeError) as excinfo:
@@ -83,12 +85,18 @@ def test_lambda_closure_cleanup():
 def test_cpp_function_roundtrip():
     """Test if passing a function pointer from C++ -> Python -> C++ yields the original pointer"""
 
-    assert m.test_dummy_function(m.dummy_function) == "matches dummy_function: eval(1) = 2"
-    assert (m.test_dummy_function(m.roundtrip(m.dummy_function)) ==
-            "matches dummy_function: eval(1) = 2")
+    assert (
+        m.test_dummy_function(m.dummy_function) == "matches dummy_function: eval(1) = 2"
+    )
+    assert (
+        m.test_dummy_function(m.roundtrip(m.dummy_function))
+        == "matches dummy_function: eval(1) = 2"
+    )
     assert m.roundtrip(None, expect_none=True) is None
-    assert (m.test_dummy_function(lambda x: x + 2) ==
-            "can't convert to function pointer: eval(1) = 3")
+    assert (
+        m.test_dummy_function(lambda x: x + 2)
+        == "can't convert to function pointer: eval(1) = 3"
+    )
 
     with pytest.raises(TypeError) as excinfo:
         m.test_dummy_function(m.dummy_function2)
@@ -96,8 +104,10 @@ def test_cpp_function_roundtrip():
 
     with pytest.raises(TypeError) as excinfo:
         m.test_dummy_function(lambda x, y: x + y)
-    assert any(s in str(excinfo.value) for s in ("missing 1 required positional argument",
-                                                 "takes exactly 2 arguments"))
+    assert any(
+        s in str(excinfo.value)
+        for s in ("missing 1 required positional argument", "takes exactly 2 arguments")
+    )
 
 
 def test_function_signatures(doc):
@@ -127,6 +137,7 @@ def test_async_callbacks():
     m.test_async_callback(gen_f(), work)
     # wait until work is done
     from time import sleep
+
     sleep(0.5)
     assert sum(res) == sum([x + 3 for x in work])
 
diff --git a/tests/test_chrono.py b/tests/test_chrono.py
index ae24b7dda..e9e24e082 100644
--- a/tests/test_chrono.py
+++ b/tests/test_chrono.py
@@ -80,22 +80,28 @@ SKIP_TZ_ENV_ON_WIN = pytest.mark.skipif(
 )
 
 
-@pytest.mark.parametrize("time1", [
-    datetime.datetime.today().time(),
-    datetime.time(0, 0, 0),
-    datetime.time(0, 0, 0, 1),
-    datetime.time(0, 28, 45, 109827),
-    datetime.time(0, 59, 59, 999999),
-    datetime.time(1, 0, 0),
-    datetime.time(5, 59, 59, 0),
-    datetime.time(5, 59, 59, 1),
-])
-@pytest.mark.parametrize("tz", [
-    None,
-    pytest.param("Europe/Brussels", marks=SKIP_TZ_ENV_ON_WIN),
-    pytest.param("Asia/Pyongyang", marks=SKIP_TZ_ENV_ON_WIN),
-    pytest.param("America/New_York", marks=SKIP_TZ_ENV_ON_WIN),
-])
+@pytest.mark.parametrize(
+    "time1",
+    [
+        datetime.datetime.today().time(),
+        datetime.time(0, 0, 0),
+        datetime.time(0, 0, 0, 1),
+        datetime.time(0, 28, 45, 109827),
+        datetime.time(0, 59, 59, 999999),
+        datetime.time(1, 0, 0),
+        datetime.time(5, 59, 59, 0),
+        datetime.time(5, 59, 59, 1),
+    ],
+)
+@pytest.mark.parametrize(
+    "tz",
+    [
+        None,
+        pytest.param("Europe/Brussels", marks=SKIP_TZ_ENV_ON_WIN),
+        pytest.param("Asia/Pyongyang", marks=SKIP_TZ_ENV_ON_WIN),
+        pytest.param("America/New_York", marks=SKIP_TZ_ENV_ON_WIN),
+    ],
+)
 def test_chrono_system_clock_roundtrip_time(time1, tz, monkeypatch):
     if tz is not None:
         monkeypatch.setenv("TZ", "/usr/share/zoneinfo/{}".format(tz))
@@ -199,7 +205,7 @@ def test_floating_point_duration():
 def test_nano_timepoint():
     time = datetime.datetime.now()
     time1 = m.test_nano_timepoint(time, datetime.timedelta(seconds=60))
-    assert(time1 == time + datetime.timedelta(seconds=60))
+    assert time1 == time + datetime.timedelta(seconds=60)
 
 
 def test_chrono_different_resolutions():
diff --git a/tests/test_class.py b/tests/test_class.py
index 10e4dd79b..c34ee8a12 100644
--- a/tests/test_class.py
+++ b/tests/test_class.py
@@ -31,8 +31,10 @@ def test_type():
     with pytest.raises(RuntimeError) as execinfo:
         m.check_type(0)
 
-    assert 'pybind11::detail::get_type_info: unable to find type info' in str(execinfo.value)
-    assert 'Invalid' in str(execinfo.value)
+    assert "pybind11::detail::get_type_info: unable to find type info" in str(
+        execinfo.value
+    )
+    assert "Invalid" in str(execinfo.value)
 
     # Currently not supported
     # See https://github.com/pybind/pybind11/issues/2486
@@ -73,18 +75,24 @@ def test_docstrings(doc):
     assert UserType.get_value.__name__ == "get_value"
     assert UserType.get_value.__module__ == "pybind11_tests"
 
-    assert doc(UserType.get_value) == """
+    assert (
+        doc(UserType.get_value)
+        == """
         get_value(self: m.UserType) -> int
 
         Get value using a method
     """
+    )
     assert doc(UserType.value) == "Get/set value using a property"
 
-    assert doc(m.NoConstructor.new_instance) == """
+    assert (
+        doc(m.NoConstructor.new_instance)
+        == """
         new_instance() -> m.class_.NoConstructor
 
         Return an instance
     """
+    )
 
 
 def test_qualname(doc):
@@ -93,51 +101,69 @@ def test_qualname(doc):
     assert m.NestBase.__qualname__ == "NestBase"
     assert m.NestBase.Nested.__qualname__ == "NestBase.Nested"
 
-    assert doc(m.NestBase.__init__) == """
+    assert (
+        doc(m.NestBase.__init__)
+        == """
         __init__(self: m.class_.NestBase) -> None
     """
-    assert doc(m.NestBase.g) == """
+    )
+    assert (
+        doc(m.NestBase.g)
+        == """
         g(self: m.class_.NestBase, arg0: m.class_.NestBase.Nested) -> None
     """
-    assert doc(m.NestBase.Nested.__init__) == """
+    )
+    assert (
+        doc(m.NestBase.Nested.__init__)
+        == """
         __init__(self: m.class_.NestBase.Nested) -> None
     """
-    assert doc(m.NestBase.Nested.fn) == """
+    )
+    assert (
+        doc(m.NestBase.Nested.fn)
+        == """
         fn(self: m.class_.NestBase.Nested, arg0: int, arg1: m.class_.NestBase, arg2: m.class_.NestBase.Nested) -> None
     """  # noqa: E501 line too long
-    assert doc(m.NestBase.Nested.fa) == """
+    )
+    assert (
+        doc(m.NestBase.Nested.fa)
+        == """
         fa(self: m.class_.NestBase.Nested, a: int, b: m.class_.NestBase, c: m.class_.NestBase.Nested) -> None
     """  # noqa: E501 line too long
+    )
     assert m.NestBase.__module__ == "pybind11_tests.class_"
     assert m.NestBase.Nested.__module__ == "pybind11_tests.class_"
 
 
 def test_inheritance(msg):
-    roger = m.Rabbit('Rabbit')
+    roger = m.Rabbit("Rabbit")
     assert roger.name() + " is a " + roger.species() == "Rabbit is a parrot"
     assert m.pet_name_species(roger) == "Rabbit is a parrot"
 
-    polly = m.Pet('Polly', 'parrot')
+    polly = m.Pet("Polly", "parrot")
     assert polly.name() + " is a " + polly.species() == "Polly is a parrot"
     assert m.pet_name_species(polly) == "Polly is a parrot"
 
-    molly = m.Dog('Molly')
+    molly = m.Dog("Molly")
     assert molly.name() + " is a " + molly.species() == "Molly is a dog"
     assert m.pet_name_species(molly) == "Molly is a dog"
 
-    fred = m.Hamster('Fred')
+    fred = m.Hamster("Fred")
     assert fred.name() + " is a " + fred.species() == "Fred is a rodent"
 
     assert m.dog_bark(molly) == "Woof!"
 
     with pytest.raises(TypeError) as excinfo:
         m.dog_bark(polly)
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         dog_bark(): incompatible function arguments. The following argument types are supported:
             1. (arg0: m.class_.Dog) -> str
 
         Invoked with: <m.class_.Pet object at 0>
     """
+    )
 
     with pytest.raises(TypeError) as excinfo:
         m.Chimera("lion", "goat")
@@ -150,6 +176,7 @@ def test_inheritance_init(msg):
     class Python(m.Pet):
         def __init__(self):
             pass
+
     with pytest.raises(TypeError) as exc_info:
         Python()
     expected = "m.class_.Pet.__init__() must be called when overriding __init__"
@@ -191,13 +218,19 @@ def test_mismatched_holder():
 
     with pytest.raises(RuntimeError) as excinfo:
         m.mismatched_holder_1()
-    assert re.match('generic_type: type ".*MismatchDerived1" does not have a non-default '
-                    'holder type while its base ".*MismatchBase1" does', str(excinfo.value))
+    assert re.match(
+        'generic_type: type ".*MismatchDerived1" does not have a non-default '
+        'holder type while its base ".*MismatchBase1" does',
+        str(excinfo.value),
+    )
 
     with pytest.raises(RuntimeError) as excinfo:
         m.mismatched_holder_2()
-    assert re.match('generic_type: type ".*MismatchDerived2" has a non-default holder type '
-                    'while its base ".*MismatchBase2" does not', str(excinfo.value))
+    assert re.match(
+        'generic_type: type ".*MismatchDerived2" has a non-default holder type '
+        'while its base ".*MismatchBase2" does not',
+        str(excinfo.value),
+    )
 
 
 def test_override_static():
@@ -229,20 +262,20 @@ def test_operator_new_delete(capture):
         a = m.HasOpNewDel()
         b = m.HasOpNewDelSize()
         d = m.HasOpNewDelBoth()
-    assert capture == """
+    assert (
+        capture
+        == """
         A new 8
         B new 4
         D new 32
     """
+    )
     sz_alias = str(m.AliasedHasOpNewDelSize.size_alias)
     sz_noalias = str(m.AliasedHasOpNewDelSize.size_noalias)
     with capture:
         c = m.AliasedHasOpNewDelSize()
         c2 = SubAliased()
-    assert capture == (
-        "C new " + sz_noalias + "\n" +
-        "C new " + sz_alias + "\n"
-    )
+    assert capture == ("C new " + sz_noalias + "\n" + "C new " + sz_alias + "\n")
 
     with capture:
         del a
@@ -251,21 +284,21 @@ def test_operator_new_delete(capture):
         pytest.gc_collect()
         del d
         pytest.gc_collect()
-    assert capture == """
+    assert (
+        capture
+        == """
         A delete
         B delete 4
         D delete
     """
+    )
 
     with capture:
         del c
         pytest.gc_collect()
         del c2
         pytest.gc_collect()
-    assert capture == (
-        "C delete " + sz_noalias + "\n" +
-        "C delete " + sz_alias + "\n"
-    )
+    assert capture == ("C delete " + sz_noalias + "\n" + "C delete " + sz_alias + "\n")
 
 
 def test_bind_protected_functions():
@@ -325,19 +358,23 @@ def test_reentrant_implicit_conversion_failure(msg):
     # ensure that there is no runaway reentrant implicit conversion (#1035)
     with pytest.raises(TypeError) as excinfo:
         m.BogusImplicitConversion(0)
-    assert msg(excinfo.value) == '''
+    assert (
+        msg(excinfo.value)
+        == """
         __init__(): incompatible constructor arguments. The following argument types are supported:
             1. m.class_.BogusImplicitConversion(arg0: m.class_.BogusImplicitConversion)
 
         Invoked with: 0
-    '''
+    """
+    )
 
 
 def test_error_after_conversions():
     with pytest.raises(TypeError) as exc_info:
         m.test_error_after_conversions("hello")
     assert str(exc_info.value).startswith(
-        "Unable to convert function return value to a Python type!")
+        "Unable to convert function return value to a Python type!"
+    )
 
 
 def test_aligned():
@@ -350,8 +387,10 @@ def test_aligned():
 @pytest.mark.xfail("env.PYPY")
 def test_final():
     with pytest.raises(TypeError) as exc_info:
+
         class PyFinalChild(m.IsFinal):
             pass
+
     assert str(exc_info.value).endswith("is not an acceptable base type")
 
 
@@ -359,8 +398,10 @@ def test_final():
 @pytest.mark.xfail("env.PYPY")
 def test_non_final_final():
     with pytest.raises(TypeError) as exc_info:
+
         class PyNonFinalFinalChild(m.IsNonFinalFinal):
             pass
+
     assert str(exc_info.value).endswith("is not an acceptable base type")
 
 
@@ -396,11 +437,14 @@ def test_base_and_derived_nested_scope():
 @pytest.mark.skip("See https://github.com/pybind/pybind11/pull/2564")
 def test_register_duplicate_class():
     import types
+
     module_scope = types.ModuleType("module_scope")
     with pytest.raises(RuntimeError) as exc_info:
         m.register_duplicate_class_name(module_scope)
-    expected = ('generic_type: cannot initialize type "Duplicate": '
-                'an object with that name is already defined')
+    expected = (
+        'generic_type: cannot initialize type "Duplicate": '
+        "an object with that name is already defined"
+    )
     assert str(exc_info.value) == expected
     with pytest.raises(RuntimeError) as exc_info:
         m.register_duplicate_class_type(module_scope)
@@ -409,10 +453,13 @@ def test_register_duplicate_class():
 
     class ClassScope:
         pass
+
     with pytest.raises(RuntimeError) as exc_info:
         m.register_duplicate_nested_class_name(ClassScope)
-    expected = ('generic_type: cannot initialize type "DuplicateNested": '
-                'an object with that name is already defined')
+    expected = (
+        'generic_type: cannot initialize type "DuplicateNested": '
+        "an object with that name is already defined"
+    )
     assert str(exc_info.value) == expected
     with pytest.raises(RuntimeError) as exc_info:
         m.register_duplicate_nested_class_type(ClassScope)
diff --git a/tests/test_copy_move.py b/tests/test_copy_move.py
index 6b53993a9..7e3cc168c 100644
--- a/tests/test_copy_move.py
+++ b/tests/test_copy_move.py
@@ -19,7 +19,11 @@ def test_move_and_copy_casts():
     """Cast some values in C++ via custom type casters and count the number of moves/copies."""
 
     cstats = m.move_and_copy_cstats()
-    c_m, c_mc, c_c = cstats["MoveOnlyInt"], cstats["MoveOrCopyInt"], cstats["CopyOnlyInt"]
+    c_m, c_mc, c_c = (
+        cstats["MoveOnlyInt"],
+        cstats["MoveOrCopyInt"],
+        cstats["CopyOnlyInt"],
+    )
 
     # The type move constructions/assignments below each get incremented: the move assignment comes
     # from the type_caster load; the move construction happens when extracting that via a cast or
@@ -43,7 +47,11 @@ def test_move_and_copy_loads():
     moves/copies."""
 
     cstats = m.move_and_copy_cstats()
-    c_m, c_mc, c_c = cstats["MoveOnlyInt"], cstats["MoveOrCopyInt"], cstats["CopyOnlyInt"]
+    c_m, c_mc, c_c = (
+        cstats["MoveOnlyInt"],
+        cstats["MoveOrCopyInt"],
+        cstats["CopyOnlyInt"],
+    )
 
     assert m.move_only(10) == 10  # 1 move, c_m
     assert m.move_or_copy(11) == 11  # 1 move, c_mc
@@ -66,12 +74,16 @@ def test_move_and_copy_loads():
     assert c_m.alive() + c_mc.alive() + c_c.alive() == 0
 
 
-@pytest.mark.skipif(not m.has_optional, reason='no <optional>')
+@pytest.mark.skipif(not m.has_optional, reason="no <optional>")
 def test_move_and_copy_load_optional():
     """Tests move/copy loads of std::optional arguments"""
 
     cstats = m.move_and_copy_cstats()
-    c_m, c_mc, c_c = cstats["MoveOnlyInt"], cstats["MoveOrCopyInt"], cstats["CopyOnlyInt"]
+    c_m, c_mc, c_c = (
+        cstats["MoveOnlyInt"],
+        cstats["MoveOrCopyInt"],
+        cstats["CopyOnlyInt"],
+    )
 
     # The extra move/copy constructions below come from the std::optional move (which has to move
     # its arguments):
diff --git a/tests/test_custom_type_casters.py b/tests/test_custom_type_casters.py
index 9475c4516..bb74d54eb 100644
--- a/tests/test_custom_type_casters.py
+++ b/tests/test_custom_type_casters.py
@@ -5,65 +5,91 @@ from pybind11_tests import custom_type_casters as m
 
 def test_noconvert_args(msg):
     a = m.ArgInspector()
-    assert msg(a.f("hi")) == """
+    assert (
+        msg(a.f("hi"))
+        == """
         loading ArgInspector1 argument WITH conversion allowed.  Argument value = hi
     """
-    assert msg(a.g("this is a", "this is b")) == """
+    )
+    assert (
+        msg(a.g("this is a", "this is b"))
+        == """
         loading ArgInspector1 argument WITHOUT conversion allowed.  Argument value = this is a
         loading ArgInspector1 argument WITH conversion allowed.  Argument value = this is b
         13
         loading ArgInspector2 argument WITH conversion allowed.  Argument value = (default arg inspector 2)
     """  # noqa: E501 line too long
-    assert msg(a.g("this is a", "this is b", 42)) == """
+    )
+    assert (
+        msg(a.g("this is a", "this is b", 42))
+        == """
         loading ArgInspector1 argument WITHOUT conversion allowed.  Argument value = this is a
         loading ArgInspector1 argument WITH conversion allowed.  Argument value = this is b
         42
         loading ArgInspector2 argument WITH conversion allowed.  Argument value = (default arg inspector 2)
     """  # noqa: E501 line too long
-    assert msg(a.g("this is a", "this is b", 42, "this is d")) == """
+    )
+    assert (
+        msg(a.g("this is a", "this is b", 42, "this is d"))
+        == """
         loading ArgInspector1 argument WITHOUT conversion allowed.  Argument value = this is a
         loading ArgInspector1 argument WITH conversion allowed.  Argument value = this is b
         42
         loading ArgInspector2 argument WITH conversion allowed.  Argument value = this is d
     """
-    assert (a.h("arg 1") ==
-            "loading ArgInspector2 argument WITHOUT conversion allowed.  Argument value = arg 1")
-    assert msg(m.arg_inspect_func("A1", "A2")) == """
+    )
+    assert (
+        a.h("arg 1")
+        == "loading ArgInspector2 argument WITHOUT conversion allowed.  Argument value = arg 1"
+    )
+    assert (
+        msg(m.arg_inspect_func("A1", "A2"))
+        == """
         loading ArgInspector2 argument WITH conversion allowed.  Argument value = A1
         loading ArgInspector1 argument WITHOUT conversion allowed.  Argument value = A2
     """
+    )
 
     assert m.floats_preferred(4) == 2.0
     assert m.floats_only(4.0) == 2.0
     with pytest.raises(TypeError) as excinfo:
         m.floats_only(4)
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         floats_only(): incompatible function arguments. The following argument types are supported:
             1. (f: float) -> float
 
         Invoked with: 4
     """
+    )
 
     assert m.ints_preferred(4) == 2
     assert m.ints_preferred(True) == 0
     with pytest.raises(TypeError) as excinfo:
         m.ints_preferred(4.0)
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         ints_preferred(): incompatible function arguments. The following argument types are supported:
             1. (i: int) -> int
 
         Invoked with: 4.0
     """  # noqa: E501 line too long
+    )
 
     assert m.ints_only(4) == 2
     with pytest.raises(TypeError) as excinfo:
         m.ints_only(4.0)
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         ints_only(): incompatible function arguments. The following argument types are supported:
             1. (i: int) -> int
 
         Invoked with: 4.0
     """
+    )
 
 
 def test_custom_caster_destruction():
diff --git a/tests/test_docstring_options.py b/tests/test_docstring_options.py
index 80ade0f15..87d80d2df 100644
--- a/tests/test_docstring_options.py
+++ b/tests/test_docstring_options.py
@@ -18,10 +18,10 @@ def test_docstring_options():
     assert m.test_overloaded3.__doc__ == "Overload docstr"
 
     # options.enable_function_signatures()
-    assert m.test_function3.__doc__ .startswith("test_function3(a: int, b: int) -> None")
+    assert m.test_function3.__doc__.startswith("test_function3(a: int, b: int) -> None")
 
-    assert m.test_function4.__doc__ .startswith("test_function4(a: int, b: int) -> None")
-    assert m.test_function4.__doc__ .endswith("A custom docstring\n")
+    assert m.test_function4.__doc__.startswith("test_function4(a: int, b: int) -> None")
+    assert m.test_function4.__doc__.endswith("A custom docstring\n")
 
     # options.disable_function_signatures()
     # options.disable_user_defined_docstrings()
@@ -31,8 +31,8 @@ def test_docstring_options():
     assert m.test_function6.__doc__ == "A custom docstring"
 
     # RAII destructor
-    assert m.test_function7.__doc__ .startswith("test_function7(a: int, b: int) -> None")
-    assert m.test_function7.__doc__ .endswith("A custom docstring\n")
+    assert m.test_function7.__doc__.startswith("test_function7(a: int, b: int) -> None")
+    assert m.test_function7.__doc__.endswith("A custom docstring\n")
 
     # Suppression of user-defined docstrings for non-function objects
     assert not m.DocstringTestFoo.__doc__
diff --git a/tests/test_eigen.py b/tests/test_eigen.py
index ac6847147..a131dc15d 100644
--- a/tests/test_eigen.py
+++ b/tests/test_eigen.py
@@ -6,11 +6,15 @@ np = pytest.importorskip("numpy")
 m = pytest.importorskip("pybind11_tests.eigen")
 
 
-ref = np.array([[ 0.,  3,  0,  0,  0, 11],
-                [22,  0,  0,  0, 17, 11],
-                [ 7,  5,  0,  1,  0, 11],
-                [ 0,  0,  0,  0,  0, 11],
-                [ 0,  0, 14,  0,  8, 11]])
+ref = np.array(
+    [
+        [0.0, 3, 0, 0, 0, 11],
+        [22, 0, 0, 0, 17, 11],
+        [7, 5, 0, 1, 0, 11],
+        [0, 0, 0, 0, 0, 11],
+        [0, 0, 14, 0, 8, 11],
+    ]
+)
 
 
 def assert_equal_ref(mat):
@@ -40,28 +44,37 @@ def test_dense():
 
 
 def test_partially_fixed():
-    ref2 = np.array([[0., 1, 2, 3], [4, 5, 6, 7], [8, 9, 10, 11], [12, 13, 14, 15]])
+    ref2 = np.array([[0.0, 1, 2, 3], [4, 5, 6, 7], [8, 9, 10, 11], [12, 13, 14, 15]])
     np.testing.assert_array_equal(m.partial_copy_four_rm_r(ref2), ref2)
     np.testing.assert_array_equal(m.partial_copy_four_rm_c(ref2), ref2)
     np.testing.assert_array_equal(m.partial_copy_four_rm_r(ref2[:, 1]), ref2[:, [1]])
     np.testing.assert_array_equal(m.partial_copy_four_rm_c(ref2[0, :]), ref2[[0], :])
-    np.testing.assert_array_equal(m.partial_copy_four_rm_r(ref2[:, (0, 2)]), ref2[:, (0, 2)])
     np.testing.assert_array_equal(
-        m.partial_copy_four_rm_c(ref2[(3, 1, 2), :]), ref2[(3, 1, 2), :])
+        m.partial_copy_four_rm_r(ref2[:, (0, 2)]), ref2[:, (0, 2)]
+    )
+    np.testing.assert_array_equal(
+        m.partial_copy_four_rm_c(ref2[(3, 1, 2), :]), ref2[(3, 1, 2), :]
+    )
 
     np.testing.assert_array_equal(m.partial_copy_four_cm_r(ref2), ref2)
     np.testing.assert_array_equal(m.partial_copy_four_cm_c(ref2), ref2)
     np.testing.assert_array_equal(m.partial_copy_four_cm_r(ref2[:, 1]), ref2[:, [1]])
     np.testing.assert_array_equal(m.partial_copy_four_cm_c(ref2[0, :]), ref2[[0], :])
-    np.testing.assert_array_equal(m.partial_copy_four_cm_r(ref2[:, (0, 2)]), ref2[:, (0, 2)])
     np.testing.assert_array_equal(
-        m.partial_copy_four_cm_c(ref2[(3, 1, 2), :]), ref2[(3, 1, 2), :])
+        m.partial_copy_four_cm_r(ref2[:, (0, 2)]), ref2[:, (0, 2)]
+    )
+    np.testing.assert_array_equal(
+        m.partial_copy_four_cm_c(ref2[(3, 1, 2), :]), ref2[(3, 1, 2), :]
+    )
 
     # TypeError should be raise for a shape mismatch
-    functions = [m.partial_copy_four_rm_r, m.partial_copy_four_rm_c,
-                 m.partial_copy_four_cm_r, m.partial_copy_four_cm_c]
-    matrix_with_wrong_shape = [[1, 2],
-                               [3, 4]]
+    functions = [
+        m.partial_copy_four_rm_r,
+        m.partial_copy_four_rm_c,
+        m.partial_copy_four_cm_r,
+        m.partial_copy_four_cm_c,
+    ]
+    matrix_with_wrong_shape = [[1, 2], [3, 4]]
     for f in functions:
         with pytest.raises(TypeError) as excinfo:
             f(matrix_with_wrong_shape)
@@ -69,7 +82,7 @@ def test_partially_fixed():
 
 
 def test_mutator_descriptors():
-    zr = np.arange(30, dtype='float32').reshape(5, 6)  # row-major
+    zr = np.arange(30, dtype="float32").reshape(5, 6)  # row-major
     zc = zr.reshape(6, 5).transpose()  # column-major
 
     m.fixed_mutator_r(zr)
@@ -78,18 +91,21 @@ def test_mutator_descriptors():
     m.fixed_mutator_a(zc)
     with pytest.raises(TypeError) as excinfo:
         m.fixed_mutator_r(zc)
-    assert ('(arg0: numpy.ndarray[numpy.float32[5, 6],'
-            ' flags.writeable, flags.c_contiguous]) -> None'
-            in str(excinfo.value))
+    assert (
+        "(arg0: numpy.ndarray[numpy.float32[5, 6],"
+        " flags.writeable, flags.c_contiguous]) -> None" in str(excinfo.value)
+    )
     with pytest.raises(TypeError) as excinfo:
         m.fixed_mutator_c(zr)
-    assert ('(arg0: numpy.ndarray[numpy.float32[5, 6],'
-            ' flags.writeable, flags.f_contiguous]) -> None'
-            in str(excinfo.value))
+    assert (
+        "(arg0: numpy.ndarray[numpy.float32[5, 6],"
+        " flags.writeable, flags.f_contiguous]) -> None" in str(excinfo.value)
+    )
     with pytest.raises(TypeError) as excinfo:
-        m.fixed_mutator_a(np.array([[1, 2], [3, 4]], dtype='float32'))
-    assert ('(arg0: numpy.ndarray[numpy.float32[5, 6], flags.writeable]) -> None'
-            in str(excinfo.value))
+        m.fixed_mutator_a(np.array([[1, 2], [3, 4]], dtype="float32"))
+    assert "(arg0: numpy.ndarray[numpy.float32[5, 6], flags.writeable]) -> None" in str(
+        excinfo.value
+    )
     zr.flags.writeable = False
     with pytest.raises(TypeError):
         m.fixed_mutator_r(zr)
@@ -98,26 +114,26 @@ def test_mutator_descriptors():
 
 
 def test_cpp_casting():
-    assert m.cpp_copy(m.fixed_r()) == 22.
-    assert m.cpp_copy(m.fixed_c()) == 22.
-    z = np.array([[5., 6], [7, 8]])
-    assert m.cpp_copy(z) == 7.
-    assert m.cpp_copy(m.get_cm_ref()) == 21.
-    assert m.cpp_copy(m.get_rm_ref()) == 21.
-    assert m.cpp_ref_c(m.get_cm_ref()) == 21.
-    assert m.cpp_ref_r(m.get_rm_ref()) == 21.
+    assert m.cpp_copy(m.fixed_r()) == 22.0
+    assert m.cpp_copy(m.fixed_c()) == 22.0
+    z = np.array([[5.0, 6], [7, 8]])
+    assert m.cpp_copy(z) == 7.0
+    assert m.cpp_copy(m.get_cm_ref()) == 21.0
+    assert m.cpp_copy(m.get_rm_ref()) == 21.0
+    assert m.cpp_ref_c(m.get_cm_ref()) == 21.0
+    assert m.cpp_ref_r(m.get_rm_ref()) == 21.0
     with pytest.raises(RuntimeError) as excinfo:
         # Can't reference m.fixed_c: it contains floats, m.cpp_ref_any wants doubles
         m.cpp_ref_any(m.fixed_c())
-    assert 'Unable to cast Python instance' in str(excinfo.value)
+    assert "Unable to cast Python instance" in str(excinfo.value)
     with pytest.raises(RuntimeError) as excinfo:
         # Can't reference m.fixed_r: it contains floats, m.cpp_ref_any wants doubles
         m.cpp_ref_any(m.fixed_r())
-    assert 'Unable to cast Python instance' in str(excinfo.value)
-    assert m.cpp_ref_any(m.ReturnTester.create()) == 1.
+    assert "Unable to cast Python instance" in str(excinfo.value)
+    assert m.cpp_ref_any(m.ReturnTester.create()) == 1.0
 
-    assert m.cpp_ref_any(m.get_cm_ref()) == 21.
-    assert m.cpp_ref_any(m.get_cm_ref()) == 21.
+    assert m.cpp_ref_any(m.get_cm_ref()) == 21.0
+    assert m.cpp_ref_any(m.get_cm_ref()) == 21.0
 
 
 def test_pass_readonly_array():
@@ -149,7 +165,7 @@ def test_nonunit_stride_from_python():
     # Mutator:
     m.double_threer(second_row)
     m.double_threec(second_col)
-    np.testing.assert_array_equal(counting_mat, [[0., 2, 2], [6, 16, 10], [6, 14, 8]])
+    np.testing.assert_array_equal(counting_mat, [[0.0, 2, 2], [6, 16, 10], [6, 14, 8]])
 
 
 def test_negative_stride_from_python(msg):
@@ -178,26 +194,36 @@ def test_negative_stride_from_python(msg):
     # Mutator:
     with pytest.raises(TypeError) as excinfo:
         m.double_threer(second_row)
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         double_threer(): incompatible function arguments. The following argument types are supported:
             1. (arg0: numpy.ndarray[numpy.float32[1, 3], flags.writeable]) -> None
 
-        Invoked with: """ + repr(np.array([ 5.,  4.,  3.], dtype='float32'))  # noqa: E501 line too long
+        Invoked with: """  # noqa: E501 line too long
+        + repr(np.array([5.0, 4.0, 3.0], dtype="float32"))
+    )
 
     with pytest.raises(TypeError) as excinfo:
         m.double_threec(second_col)
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         double_threec(): incompatible function arguments. The following argument types are supported:
             1. (arg0: numpy.ndarray[numpy.float32[3, 1], flags.writeable]) -> None
 
-        Invoked with: """ + repr(np.array([ 7.,  4.,  1.], dtype='float32'))  # noqa: E501 line too long
+        Invoked with: """  # noqa: E501 line too long
+        + repr(np.array([7.0, 4.0, 1.0], dtype="float32"))
+    )
 
 
 def test_nonunit_stride_to_python():
     assert np.all(m.diagonal(ref) == ref.diagonal())
     assert np.all(m.diagonal_1(ref) == ref.diagonal(1))
     for i in range(-5, 7):
-        assert np.all(m.diagonal_n(ref, i) == ref.diagonal(i)), "m.diagonal_n({})".format(i)
+        assert np.all(
+            m.diagonal_n(ref, i) == ref.diagonal(i)
+        ), "m.diagonal_n({})".format(i)
 
     assert np.all(m.block(ref, 2, 1, 3, 3) == ref[2:5, 1:4])
     assert np.all(m.block(ref, 1, 4, 4, 2) == ref[1:, 4:])
@@ -207,8 +233,10 @@ def test_nonunit_stride_to_python():
 def test_eigen_ref_to_python():
     chols = [m.cholesky1, m.cholesky2, m.cholesky3, m.cholesky4]
     for i, chol in enumerate(chols, start=1):
-        mymat = chol(np.array([[1., 2, 4], [2, 13, 23], [4, 23, 77]]))
-        assert np.all(mymat == np.array([[1, 0, 0], [2, 3, 0], [4, 5, 6]])), "cholesky{}".format(i)
+        mymat = chol(np.array([[1.0, 2, 4], [2, 13, 23], [4, 23, 77]]))
+        assert np.all(
+            mymat == np.array([[1, 0, 0], [2, 3, 0], [4, 5, 6]])
+        ), "cholesky{}".format(i)
 
 
 def assign_both(a1, a2, r, c, v):
@@ -325,8 +353,12 @@ def test_eigen_return_references():
     np.testing.assert_array_equal(a_block1, master[3:5, 3:5])
     np.testing.assert_array_equal(a_block2, master[2:5, 2:4])
     np.testing.assert_array_equal(a_block3, master[6:10, 7:10])
-    np.testing.assert_array_equal(a_corn1, master[0::master.shape[0] - 1, 0::master.shape[1] - 1])
-    np.testing.assert_array_equal(a_corn2, master[0::master.shape[0] - 1, 0::master.shape[1] - 1])
+    np.testing.assert_array_equal(
+        a_corn1, master[0 :: master.shape[0] - 1, 0 :: master.shape[1] - 1]
+    )
+    np.testing.assert_array_equal(
+        a_corn2, master[0 :: master.shape[0] - 1, 0 :: master.shape[1] - 1]
+    )
 
     np.testing.assert_array_equal(a_copy1, c1want)
     np.testing.assert_array_equal(a_copy2, c2want)
@@ -355,16 +387,28 @@ def test_eigen_keepalive():
     cstats = ConstructorStats.get(m.ReturnTester)
     assert cstats.alive() == 1
     unsafe = [a.ref(), a.ref_const(), a.block(1, 2, 3, 4)]
-    copies = [a.copy_get(), a.copy_view(), a.copy_ref(), a.copy_ref_const(),
-              a.copy_block(4, 3, 2, 1)]
+    copies = [
+        a.copy_get(),
+        a.copy_view(),
+        a.copy_ref(),
+        a.copy_ref_const(),
+        a.copy_block(4, 3, 2, 1),
+    ]
     del a
     assert cstats.alive() == 0
     del unsafe
     del copies
 
-    for meth in [m.ReturnTester.get, m.ReturnTester.get_ptr, m.ReturnTester.view,
-                 m.ReturnTester.view_ptr, m.ReturnTester.ref_safe, m.ReturnTester.ref_const_safe,
-                 m.ReturnTester.corners, m.ReturnTester.corners_const]:
+    for meth in [
+        m.ReturnTester.get,
+        m.ReturnTester.get_ptr,
+        m.ReturnTester.view,
+        m.ReturnTester.view_ptr,
+        m.ReturnTester.ref_safe,
+        m.ReturnTester.ref_const_safe,
+        m.ReturnTester.corners,
+        m.ReturnTester.corners_const,
+    ]:
         assert_keeps_alive(m.ReturnTester, meth)
 
     for meth in [m.ReturnTester.block_safe, m.ReturnTester.block_const]:
@@ -374,18 +418,18 @@ def test_eigen_keepalive():
 def test_eigen_ref_mutators():
     """Tests Eigen's ability to mutate numpy values"""
 
-    orig = np.array([[1., 2, 3], [4, 5, 6], [7, 8, 9]])
+    orig = np.array([[1.0, 2, 3], [4, 5, 6], [7, 8, 9]])
     zr = np.array(orig)
-    zc = np.array(orig, order='F')
+    zc = np.array(orig, order="F")
     m.add_rm(zr, 1, 0, 100)
-    assert np.all(zr == np.array([[1., 2, 3], [104, 5, 6], [7, 8, 9]]))
+    assert np.all(zr == np.array([[1.0, 2, 3], [104, 5, 6], [7, 8, 9]]))
     m.add_cm(zc, 1, 0, 200)
-    assert np.all(zc == np.array([[1., 2, 3], [204, 5, 6], [7, 8, 9]]))
+    assert np.all(zc == np.array([[1.0, 2, 3], [204, 5, 6], [7, 8, 9]]))
 
     m.add_any(zr, 1, 0, 20)
-    assert np.all(zr == np.array([[1., 2, 3], [124, 5, 6], [7, 8, 9]]))
+    assert np.all(zr == np.array([[1.0, 2, 3], [124, 5, 6], [7, 8, 9]]))
     m.add_any(zc, 1, 0, 10)
-    assert np.all(zc == np.array([[1., 2, 3], [214, 5, 6], [7, 8, 9]]))
+    assert np.all(zc == np.array([[1.0, 2, 3], [214, 5, 6], [7, 8, 9]]))
 
     # Can't reference a col-major array with a row-major Ref, and vice versa:
     with pytest.raises(TypeError):
@@ -406,8 +450,8 @@ def test_eigen_ref_mutators():
     cornersr = zr[0::2, 0::2]
     cornersc = zc[0::2, 0::2]
 
-    assert np.all(cornersr == np.array([[1., 3], [7, 9]]))
-    assert np.all(cornersc == np.array([[1., 3], [7, 9]]))
+    assert np.all(cornersr == np.array([[1.0, 3], [7, 9]]))
+    assert np.all(cornersc == np.array([[1.0, 3], [7, 9]]))
 
     with pytest.raises(TypeError):
         m.add_rm(cornersr, 0, 1, 25)
@@ -419,8 +463,8 @@ def test_eigen_ref_mutators():
         m.add_cm(cornersc, 0, 1, 25)
     m.add_any(cornersr, 0, 1, 25)
     m.add_any(cornersc, 0, 1, 44)
-    assert np.all(zr == np.array([[1., 2, 28], [4, 5, 6], [7, 8, 9]]))
-    assert np.all(zc == np.array([[1., 2, 47], [4, 5, 6], [7, 8, 9]]))
+    assert np.all(zr == np.array([[1.0, 2, 28], [4, 5, 6], [7, 8, 9]]))
+    assert np.all(zc == np.array([[1.0, 2, 47], [4, 5, 6], [7, 8, 9]]))
 
     # You shouldn't be allowed to pass a non-writeable array to a mutating Eigen method:
     zro = zr[0:4, 0:4]
@@ -458,7 +502,7 @@ def test_numpy_ref_mutators():
     assert not zrro.flags.owndata and not zrro.flags.writeable
 
     zc[1, 2] = 99
-    expect = np.array([[11., 12, 13], [21, 22, 99], [31, 32, 33]])
+    expect = np.array([[11.0, 12, 13], [21, 22, 99], [31, 32, 33]])
     # We should have just changed zc, of course, but also zcro and the original eigen matrix
     assert np.all(zc == expect)
     assert np.all(zcro == expect)
@@ -506,18 +550,20 @@ def test_both_ref_mutators():
     assert np.all(z == z3)
     assert np.all(z == z4)
     assert np.all(z == z5)
-    expect = np.array([[0., 22, 20], [31, 37, 33], [41, 42, 38]])
+    expect = np.array([[0.0, 22, 20], [31, 37, 33], [41, 42, 38]])
     assert np.all(z == expect)
 
-    y = np.array(range(100), dtype='float64').reshape(10, 10)
+    y = np.array(range(100), dtype="float64").reshape(10, 10)
     y2 = m.incr_matrix_any(y, 10)  # np -> eigen -> np
-    y3 = m.incr_matrix_any(y2[0::2, 0::2], -33)  # np -> eigen -> np slice -> np -> eigen -> np
+    y3 = m.incr_matrix_any(
+        y2[0::2, 0::2], -33
+    )  # np -> eigen -> np slice -> np -> eigen -> np
     y4 = m.even_rows(y3)  # numpy -> eigen slice -> (... y3)
     y5 = m.even_cols(y4)  # numpy -> eigen slice -> (... y4)
     y6 = m.incr_matrix_any(y5, 1000)  # numpy -> eigen -> (... y5)
 
     # Apply same mutations using just numpy:
-    yexpect = np.array(range(100), dtype='float64').reshape(10, 10)
+    yexpect = np.array(range(100), dtype="float64").reshape(10, 10)
     yexpect += 10
     yexpect[0::2, 0::2] -= 33
     yexpect[0::4, 0::4] += 1000
@@ -532,10 +578,14 @@ def test_both_ref_mutators():
 def test_nocopy_wrapper():
     # get_elem requires a column-contiguous matrix reference, but should be
     # callable with other types of matrix (via copying):
-    int_matrix_colmajor = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]], order='F')
-    dbl_matrix_colmajor = np.array(int_matrix_colmajor, dtype='double', order='F', copy=True)
-    int_matrix_rowmajor = np.array(int_matrix_colmajor, order='C', copy=True)
-    dbl_matrix_rowmajor = np.array(int_matrix_rowmajor, dtype='double', order='C', copy=True)
+    int_matrix_colmajor = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]], order="F")
+    dbl_matrix_colmajor = np.array(
+        int_matrix_colmajor, dtype="double", order="F", copy=True
+    )
+    int_matrix_rowmajor = np.array(int_matrix_colmajor, order="C", copy=True)
+    dbl_matrix_rowmajor = np.array(
+        int_matrix_rowmajor, dtype="double", order="C", copy=True
+    )
 
     # All should be callable via get_elem:
     assert m.get_elem(int_matrix_colmajor) == 8
@@ -546,32 +596,38 @@ def test_nocopy_wrapper():
     # All but the second should fail with m.get_elem_nocopy:
     with pytest.raises(TypeError) as excinfo:
         m.get_elem_nocopy(int_matrix_colmajor)
-    assert ('get_elem_nocopy(): incompatible function arguments.' in str(excinfo.value) and
-            ', flags.f_contiguous' in str(excinfo.value))
+    assert "get_elem_nocopy(): incompatible function arguments." in str(
+        excinfo.value
+    ) and ", flags.f_contiguous" in str(excinfo.value)
     assert m.get_elem_nocopy(dbl_matrix_colmajor) == 8
     with pytest.raises(TypeError) as excinfo:
         m.get_elem_nocopy(int_matrix_rowmajor)
-    assert ('get_elem_nocopy(): incompatible function arguments.' in str(excinfo.value) and
-            ', flags.f_contiguous' in str(excinfo.value))
+    assert "get_elem_nocopy(): incompatible function arguments." in str(
+        excinfo.value
+    ) and ", flags.f_contiguous" in str(excinfo.value)
     with pytest.raises(TypeError) as excinfo:
         m.get_elem_nocopy(dbl_matrix_rowmajor)
-    assert ('get_elem_nocopy(): incompatible function arguments.' in str(excinfo.value) and
-            ', flags.f_contiguous' in str(excinfo.value))
+    assert "get_elem_nocopy(): incompatible function arguments." in str(
+        excinfo.value
+    ) and ", flags.f_contiguous" in str(excinfo.value)
 
     # For the row-major test, we take a long matrix in row-major, so only the third is allowed:
     with pytest.raises(TypeError) as excinfo:
         m.get_elem_rm_nocopy(int_matrix_colmajor)
-    assert ('get_elem_rm_nocopy(): incompatible function arguments.' in str(excinfo.value) and
-            ', flags.c_contiguous' in str(excinfo.value))
+    assert "get_elem_rm_nocopy(): incompatible function arguments." in str(
+        excinfo.value
+    ) and ", flags.c_contiguous" in str(excinfo.value)
     with pytest.raises(TypeError) as excinfo:
         m.get_elem_rm_nocopy(dbl_matrix_colmajor)
-    assert ('get_elem_rm_nocopy(): incompatible function arguments.' in str(excinfo.value) and
-            ', flags.c_contiguous' in str(excinfo.value))
+    assert "get_elem_rm_nocopy(): incompatible function arguments." in str(
+        excinfo.value
+    ) and ", flags.c_contiguous" in str(excinfo.value)
     assert m.get_elem_rm_nocopy(int_matrix_rowmajor) == 8
     with pytest.raises(TypeError) as excinfo:
         m.get_elem_rm_nocopy(dbl_matrix_rowmajor)
-    assert ('get_elem_rm_nocopy(): incompatible function arguments.' in str(excinfo.value) and
-            ', flags.c_contiguous' in str(excinfo.value))
+    assert "get_elem_rm_nocopy(): incompatible function arguments." in str(
+        excinfo.value
+    ) and ", flags.c_contiguous" in str(excinfo.value)
 
 
 def test_eigen_ref_life_support():
@@ -589,12 +645,9 @@ def test_eigen_ref_life_support():
 
 
 def test_special_matrix_objects():
-    assert np.all(m.incr_diag(7) == np.diag([1., 2, 3, 4, 5, 6, 7]))
+    assert np.all(m.incr_diag(7) == np.diag([1.0, 2, 3, 4, 5, 6, 7]))
 
-    asymm = np.array([[ 1.,  2,  3,  4],
-                      [ 5,  6,  7,  8],
-                      [ 9, 10, 11, 12],
-                      [13, 14, 15, 16]])
+    asymm = np.array([[1.0, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]])
     symm_lower = np.array(asymm)
     symm_upper = np.array(asymm)
     for i in range(4):
@@ -607,41 +660,51 @@ def test_special_matrix_objects():
 
 
 def test_dense_signature(doc):
-    assert doc(m.double_col) == """
+    assert (
+        doc(m.double_col)
+        == """
         double_col(arg0: numpy.ndarray[numpy.float32[m, 1]]) -> numpy.ndarray[numpy.float32[m, 1]]
     """
-    assert doc(m.double_row) == """
+    )
+    assert (
+        doc(m.double_row)
+        == """
         double_row(arg0: numpy.ndarray[numpy.float32[1, n]]) -> numpy.ndarray[numpy.float32[1, n]]
     """
-    assert doc(m.double_complex) == ("""
+    )
+    assert doc(m.double_complex) == (
+        """
         double_complex(arg0: numpy.ndarray[numpy.complex64[m, 1]])"""
-                                     """ -> numpy.ndarray[numpy.complex64[m, 1]]
-    """)
-    assert doc(m.double_mat_rm) == ("""
+        """ -> numpy.ndarray[numpy.complex64[m, 1]]
+    """
+    )
+    assert doc(m.double_mat_rm) == (
+        """
         double_mat_rm(arg0: numpy.ndarray[numpy.float32[m, n]])"""
-                                    """ -> numpy.ndarray[numpy.float32[m, n]]
-    """)
+        """ -> numpy.ndarray[numpy.float32[m, n]]
+    """
+    )
 
 
 def test_named_arguments():
     a = np.array([[1.0, 2], [3, 4], [5, 6]])
     b = np.ones((2, 1))
 
-    assert np.all(m.matrix_multiply(a, b) == np.array([[3.], [7], [11]]))
-    assert np.all(m.matrix_multiply(A=a, B=b) == np.array([[3.], [7], [11]]))
-    assert np.all(m.matrix_multiply(B=b, A=a) == np.array([[3.], [7], [11]]))
+    assert np.all(m.matrix_multiply(a, b) == np.array([[3.0], [7], [11]]))
+    assert np.all(m.matrix_multiply(A=a, B=b) == np.array([[3.0], [7], [11]]))
+    assert np.all(m.matrix_multiply(B=b, A=a) == np.array([[3.0], [7], [11]]))
 
     with pytest.raises(ValueError) as excinfo:
         m.matrix_multiply(b, a)
-    assert str(excinfo.value) == 'Nonconformable matrices!'
+    assert str(excinfo.value) == "Nonconformable matrices!"
 
     with pytest.raises(ValueError) as excinfo:
         m.matrix_multiply(A=b, B=a)
-    assert str(excinfo.value) == 'Nonconformable matrices!'
+    assert str(excinfo.value) == "Nonconformable matrices!"
 
     with pytest.raises(ValueError) as excinfo:
         m.matrix_multiply(B=a, A=b)
-    assert str(excinfo.value) == 'Nonconformable matrices!'
+    assert str(excinfo.value) == "Nonconformable matrices!"
 
 
 def test_sparse():
@@ -656,21 +719,31 @@ def test_sparse():
 
 def test_sparse_signature(doc):
     pytest.importorskip("scipy")
-    assert doc(m.sparse_copy_r) == """
+    assert (
+        doc(m.sparse_copy_r)
+        == """
         sparse_copy_r(arg0: scipy.sparse.csr_matrix[numpy.float32]) -> scipy.sparse.csr_matrix[numpy.float32]
     """  # noqa: E501 line too long
-    assert doc(m.sparse_copy_c) == """
+    )
+    assert (
+        doc(m.sparse_copy_c)
+        == """
         sparse_copy_c(arg0: scipy.sparse.csc_matrix[numpy.float32]) -> scipy.sparse.csc_matrix[numpy.float32]
     """  # noqa: E501 line too long
+    )
 
 
 def test_issue738():
     """Ignore strides on a length-1 dimension (even if they would be incompatible length > 1)"""
-    assert np.all(m.iss738_f1(np.array([[1., 2, 3]])) == np.array([[1., 102, 203]]))
-    assert np.all(m.iss738_f1(np.array([[1.], [2], [3]])) == np.array([[1.], [12], [23]]))
+    assert np.all(m.iss738_f1(np.array([[1.0, 2, 3]])) == np.array([[1.0, 102, 203]]))
+    assert np.all(
+        m.iss738_f1(np.array([[1.0], [2], [3]])) == np.array([[1.0], [12], [23]])
+    )
 
-    assert np.all(m.iss738_f2(np.array([[1., 2, 3]])) == np.array([[1., 102, 203]]))
-    assert np.all(m.iss738_f2(np.array([[1.], [2], [3]])) == np.array([[1.], [12], [23]]))
+    assert np.all(m.iss738_f2(np.array([[1.0, 2, 3]])) == np.array([[1.0, 102, 203]]))
+    assert np.all(
+        m.iss738_f2(np.array([[1.0], [2], [3]])) == np.array([[1.0], [12], [23]])
+    )
 
 
 def test_issue1105():
diff --git a/tests/test_enum.py b/tests/test_enum.py
index 46cb37946..385fbbc9e 100644
--- a/tests/test_enum.py
+++ b/tests/test_enum.py
@@ -24,18 +24,24 @@ def test_unscoped_enum():
     assert m.UnscopedEnum.EOne.name == "EOne"
 
     # __members__ property
-    assert m.UnscopedEnum.__members__ == \
-        {"EOne": m.UnscopedEnum.EOne, "ETwo": m.UnscopedEnum.ETwo, "EThree": m.UnscopedEnum.EThree}
+    assert m.UnscopedEnum.__members__ == {
+        "EOne": m.UnscopedEnum.EOne,
+        "ETwo": m.UnscopedEnum.ETwo,
+        "EThree": m.UnscopedEnum.EThree,
+    }
     # __members__ readonly
     with pytest.raises(AttributeError):
         m.UnscopedEnum.__members__ = {}
     # __members__ returns a copy
     foo = m.UnscopedEnum.__members__
     foo["bar"] = "baz"
-    assert m.UnscopedEnum.__members__ == \
-        {"EOne": m.UnscopedEnum.EOne, "ETwo": m.UnscopedEnum.ETwo, "EThree": m.UnscopedEnum.EThree}
+    assert m.UnscopedEnum.__members__ == {
+        "EOne": m.UnscopedEnum.EOne,
+        "ETwo": m.UnscopedEnum.ETwo,
+        "EThree": m.UnscopedEnum.EThree,
+    }
 
-    for docstring_line in '''An unscoped enumeration
+    for docstring_line in """An unscoped enumeration
 
 Members:
 
@@ -43,7 +49,9 @@ Members:
 
   ETwo : Docstring for ETwo
 
-  EThree : Docstring for EThree'''.split('\n'):
+  EThree : Docstring for EThree""".split(
+        "\n"
+    ):
         assert docstring_line in m.UnscopedEnum.__doc__
 
     # Unscoped enums will accept ==/!= int comparisons
@@ -53,10 +61,10 @@ Members:
     assert y != 3
     assert 3 != y
     # Compare with None
-    assert (y != None)  # noqa: E711
+    assert y != None  # noqa: E711
     assert not (y == None)  # noqa: E711
     # Compare with an object
-    assert (y != object())
+    assert y != object()
     assert not (y == object())
     # Compare with string
     assert y != "2"
@@ -119,10 +127,10 @@ def test_scoped_enum():
     assert z != 3
     assert 3 != z
     # Compare with None
-    assert (z != None)  # noqa: E711
+    assert z != None  # noqa: E711
     assert not (z == None)  # noqa: E711
     # Compare with an object
-    assert (z != object())
+    assert z != object()
     assert not (z == object())
     # Scoped enums will *NOT* accept >, <, >= and <= int comparisons (Will throw exceptions)
     with pytest.raises(TypeError):
diff --git a/tests/test_eval_call.py b/tests/test_eval_call.py
index d42a0a6d3..373b67bac 100644
--- a/tests/test_eval_call.py
+++ b/tests/test_eval_call.py
@@ -1,5 +1,5 @@
 # -*- coding: utf-8 -*-
 # This file is called from 'test_eval.py'
 
-if 'call_test2' in locals():
+if "call_test2" in locals():
     call_test2(y)  # noqa: F821 undefined name
diff --git a/tests/test_exceptions.py b/tests/test_exceptions.py
index 7d7088d00..95eac7092 100644
--- a/tests/test_exceptions.py
+++ b/tests/test_exceptions.py
@@ -54,27 +54,27 @@ def test_python_alreadyset_in_destructor(monkeypatch, capsys):
     hooked = False
     triggered = [False]  # mutable, so Python 2.7 closure can modify it
 
-    if hasattr(sys, 'unraisablehook'):  # Python 3.8+
+    if hasattr(sys, "unraisablehook"):  # Python 3.8+
         hooked = True
         default_hook = sys.unraisablehook
 
         def hook(unraisable_hook_args):
             exc_type, exc_value, exc_tb, err_msg, obj = unraisable_hook_args
-            if obj == 'already_set demo':
+            if obj == "already_set demo":
                 triggered[0] = True
             default_hook(unraisable_hook_args)
             return
 
         # Use monkeypatch so pytest can apply and remove the patch as appropriate
-        monkeypatch.setattr(sys, 'unraisablehook', hook)
+        monkeypatch.setattr(sys, "unraisablehook", hook)
 
-    assert m.python_alreadyset_in_destructor('already_set demo') is True
+    assert m.python_alreadyset_in_destructor("already_set demo") is True
     if hooked:
         assert triggered[0] is True
 
     _, captured_stderr = capsys.readouterr()
     # Error message is different in Python 2 and 3, check for words that appear in both
-    assert 'ignored' in captured_stderr and 'already_set demo' in captured_stderr
+    assert "ignored" in captured_stderr and "already_set demo" in captured_stderr
 
 
 def test_exception_matches():
@@ -107,7 +107,9 @@ def test_custom(msg):
     # Can we fall-through to the default handler?
     with pytest.raises(RuntimeError) as excinfo:
         m.throws_logic_error()
-    assert msg(excinfo.value) == "this error should fall through to the standard handler"
+    assert (
+        msg(excinfo.value) == "this error should fall through to the standard handler"
+    )
 
     # OverFlow error translation.
     with pytest.raises(OverflowError) as excinfo:
@@ -166,7 +168,13 @@ def test_nested_throws(capture):
     # C++ -> Python -> C++ -> Python
     with capture:
         m.try_catch(
-            m.MyException5, pycatch, m.MyException, m.try_catch, m.MyException, throw_myex5)
+            m.MyException5,
+            pycatch,
+            m.MyException,
+            m.try_catch,
+            m.MyException,
+            throw_myex5,
+        )
     assert str(capture).startswith("MyException5: nested error 5")
 
     # C++ -> Python -> C++
@@ -182,7 +190,6 @@ def test_nested_throws(capture):
 
 # This can often happen if you wrap a pybind11 class in a Python wrapper
 def test_invalid_repr():
-
     class MyRepr(object):
         def __repr__(self):
             raise AttributeError("Example error")
diff --git a/tests/test_factory_constructors.py b/tests/test_factory_constructors.py
index b141c13de..ffcce6fd4 100644
--- a/tests/test_factory_constructors.py
+++ b/tests/test_factory_constructors.py
@@ -12,7 +12,10 @@ from pybind11_tests import ConstructorStats
 def test_init_factory_basic():
     """Tests py::init_factory() wrapper around various ways of returning the object"""
 
-    cstats = [ConstructorStats.get(c) for c in [m.TestFactory1, m.TestFactory2, m.TestFactory3]]
+    cstats = [
+        ConstructorStats.get(c)
+        for c in [m.TestFactory1, m.TestFactory2, m.TestFactory3]
+    ]
     cstats[0].alive()  # force gc
     n_inst = ConstructorStats.detail_reg_inst()
 
@@ -41,12 +44,12 @@ def test_init_factory_basic():
     z3 = m.TestFactory3("bye")
     assert z3.value == "bye"
 
-    for null_ptr_kind in [tag.null_ptr,
-                          tag.null_unique_ptr,
-                          tag.null_shared_ptr]:
+    for null_ptr_kind in [tag.null_ptr, tag.null_unique_ptr, tag.null_shared_ptr]:
         with pytest.raises(TypeError) as excinfo:
             m.TestFactory3(null_ptr_kind)
-        assert str(excinfo.value) == "pybind11::init(): factory function returned nullptr"
+        assert (
+            str(excinfo.value) == "pybind11::init(): factory function returned nullptr"
+        )
 
     assert [i.alive() for i in cstats] == [3, 3, 3]
     assert ConstructorStats.detail_reg_inst() == n_inst + 9
@@ -61,7 +64,7 @@ def test_init_factory_basic():
     assert [i.values() for i in cstats] == [
         ["3", "hi!"],
         ["7", "hi again"],
-        ["42", "bye"]
+        ["42", "bye"],
     ]
     assert [i.default_constructions for i in cstats] == [1, 1, 1]
 
@@ -69,7 +72,9 @@ def test_init_factory_basic():
 def test_init_factory_signature(msg):
     with pytest.raises(TypeError) as excinfo:
         m.TestFactory1("invalid", "constructor", "arguments")
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         __init__(): incompatible constructor arguments. The following argument types are supported:
             1. m.factory_constructors.TestFactory1(arg0: m.factory_constructors.tag.unique_ptr_tag, arg1: int)
             2. m.factory_constructors.TestFactory1(arg0: str)
@@ -78,8 +83,11 @@ def test_init_factory_signature(msg):
 
         Invoked with: 'invalid', 'constructor', 'arguments'
     """  # noqa: E501 line too long
+    )
 
-    assert msg(m.TestFactory1.__init__.__doc__) == """
+    assert (
+        msg(m.TestFactory1.__init__.__doc__)
+        == """
         __init__(*args, **kwargs)
         Overloaded function.
 
@@ -91,12 +99,16 @@ def test_init_factory_signature(msg):
 
         4. __init__(self: m.factory_constructors.TestFactory1, arg0: handle, arg1: int, arg2: handle) -> None
     """  # noqa: E501 line too long
+    )
 
 
 def test_init_factory_casting():
     """Tests py::init_factory() wrapper with various upcasting and downcasting returns"""
 
-    cstats = [ConstructorStats.get(c) for c in [m.TestFactory3, m.TestFactory4, m.TestFactory5]]
+    cstats = [
+        ConstructorStats.get(c)
+        for c in [m.TestFactory3, m.TestFactory4, m.TestFactory5]
+    ]
     cstats[0].alive()  # force gc
     n_inst = ConstructorStats.detail_reg_inst()
 
@@ -134,7 +146,7 @@ def test_init_factory_casting():
     assert [i.values() for i in cstats] == [
         ["4", "5", "6", "7", "8"],
         ["4", "5", "8"],
-        ["6", "7"]
+        ["6", "7"],
     ]
 
 
@@ -204,7 +216,7 @@ def test_init_factory_alias():
 
     assert [i.values() for i in cstats] == [
         ["1", "8", "3", "4", "5", "6", "123", "10", "47"],
-        ["hi there", "3", "4", "6", "move", "123", "why hello!", "move", "47"]
+        ["hi there", "3", "4", "6", "move", "123", "why hello!", "move", "47"],
     ]
 
 
@@ -268,9 +280,11 @@ def test_init_factory_dual():
     assert not g1.has_alias()
     with pytest.raises(TypeError) as excinfo:
         PythFactory7(tag.shared_ptr, tag.invalid_base, 14)
-    assert (str(excinfo.value) ==
-            "pybind11::init(): construction failed: returned holder-wrapped instance is not an "
-            "alias instance")
+    assert (
+        str(excinfo.value)
+        == "pybind11::init(): construction failed: returned holder-wrapped instance is not an "
+        "alias instance"
+    )
 
     assert [i.alive() for i in cstats] == [13, 7]
     assert ConstructorStats.detail_reg_inst() == n_inst + 13
@@ -284,7 +298,7 @@ def test_init_factory_dual():
 
     assert [i.values() for i in cstats] == [
         ["1", "2", "3", "4", "5", "6", "7", "8", "9", "100", "11", "12", "13", "14"],
-        ["2", "4", "6", "8", "9", "100", "12"]
+        ["2", "4", "6", "8", "9", "100", "12"],
     ]
 
 
@@ -294,7 +308,7 @@ def test_no_placement_new(capture):
     with capture:
         a = m.NoPlacementNew(123)
 
-    found = re.search(r'^operator new called, returning (\d+)\n$', str(capture))
+    found = re.search(r"^operator new called, returning (\d+)\n$", str(capture))
     assert found
     assert a.i == 123
     with capture:
@@ -305,7 +319,7 @@ def test_no_placement_new(capture):
     with capture:
         b = m.NoPlacementNew()
 
-    found = re.search(r'^operator new called, returning (\d+)\n$', str(capture))
+    found = re.search(r"^operator new called, returning (\d+)\n$", str(capture))
     assert found
     assert b.i == 100
     with capture:
@@ -333,7 +347,7 @@ def create_and_destroy(*args):
 
 
 def strip_comments(s):
-    return re.sub(r'\s+#.*', '', s)
+    return re.sub(r"\s+#.*", "", s)
 
 
 def test_reallocation_a(capture, msg):
@@ -345,7 +359,9 @@ def test_reallocation_a(capture, msg):
 
     with capture:
         create_and_destroy(1)
-    assert msg(capture) == """
+    assert (
+        msg(capture)
+        == """
         noisy new
         noisy placement new
         NoisyAlloc(int 1)
@@ -353,12 +369,14 @@ def test_reallocation_a(capture, msg):
         ~NoisyAlloc()
         noisy delete
     """
+    )
 
 
 def test_reallocation_b(capture, msg):
     with capture:
         create_and_destroy(1.5)
-    assert msg(capture) == strip_comments("""
+    assert msg(capture) == strip_comments(
+        """
         noisy new               # allocation required to attempt first overload
         noisy delete            # have to dealloc before considering factory init overload
         noisy new               # pointer factory calling "new", part 1: allocation
@@ -366,51 +384,59 @@ def test_reallocation_b(capture, msg):
         ---
         ~NoisyAlloc()  # Destructor
         noisy delete   # operator delete
-    """)
+    """
+    )
 
 
 def test_reallocation_c(capture, msg):
     with capture:
         create_and_destroy(2, 3)
-    assert msg(capture) == strip_comments("""
+    assert msg(capture) == strip_comments(
+        """
         noisy new          # pointer factory calling "new", allocation
         NoisyAlloc(int 2)  # constructor
         ---
         ~NoisyAlloc()  # Destructor
         noisy delete   # operator delete
-    """)
+    """
+    )
 
 
 def test_reallocation_d(capture, msg):
     with capture:
         create_and_destroy(2.5, 3)
-    assert msg(capture) == strip_comments("""
+    assert msg(capture) == strip_comments(
+        """
         NoisyAlloc(double 2.5)  # construction (local func variable: operator_new not called)
         noisy new               # return-by-value "new" part 1: allocation
         ~NoisyAlloc()           # moved-away local func variable destruction
         ---
         ~NoisyAlloc()  # Destructor
         noisy delete   # operator delete
-    """)
+    """
+    )
 
 
 def test_reallocation_e(capture, msg):
     with capture:
         create_and_destroy(3.5, 4.5)
-    assert msg(capture) == strip_comments("""
+    assert msg(capture) == strip_comments(
+        """
         noisy new               # preallocation needed before invoking placement-new overload
         noisy placement new     # Placement new
         NoisyAlloc(double 3.5)  # construction
         ---
         ~NoisyAlloc()  # Destructor
         noisy delete   # operator delete
-    """)
+    """
+    )
 
 
 def test_reallocation_f(capture, msg):
     with capture:
         create_and_destroy(4, 0.5)
-    assert msg(capture) == strip_comments("""
+    assert msg(capture) == strip_comments(
+        """
         noisy new          # preallocation needed before invoking placement-new overload
         noisy delete       # deallocation of preallocated storage
         noisy new          # Factory pointer allocation
@@ -418,13 +444,15 @@ def test_reallocation_f(capture, msg):
         ---
         ~NoisyAlloc()  # Destructor
         noisy delete   # operator delete
-    """)
+    """
+    )
 
 
 def test_reallocation_g(capture, msg):
     with capture:
         create_and_destroy(5, "hi")
-    assert msg(capture) == strip_comments("""
+    assert msg(capture) == strip_comments(
+        """
         noisy new            # preallocation needed before invoking first placement new
         noisy delete         # delete before considering new-style constructor
         noisy new            # preallocation for second placement new
@@ -433,13 +461,15 @@ def test_reallocation_g(capture, msg):
         ---
         ~NoisyAlloc()  # Destructor
         noisy delete   # operator delete
-    """)
+    """
+    )
 
 
 @pytest.mark.skipif("env.PY2")
 def test_invalid_self():
     """Tests invocation of the pybind-registered base class with an invalid `self` argument.  You
     can only actually do this on Python 3: Python 2 raises an exception itself if you try."""
+
     class NotPybindDerived(object):
         pass
 
@@ -463,16 +493,26 @@ def test_invalid_self():
                 a = m.TestFactory2(tag.pointer, 1)
                 m.TestFactory6.__init__(a, tag.alias, 1)
             elif bad == 3:
-                m.TestFactory6.__init__(NotPybindDerived.__new__(NotPybindDerived), tag.base, 1)
+                m.TestFactory6.__init__(
+                    NotPybindDerived.__new__(NotPybindDerived), tag.base, 1
+                )
             elif bad == 4:
-                m.TestFactory6.__init__(NotPybindDerived.__new__(NotPybindDerived), tag.alias, 1)
+                m.TestFactory6.__init__(
+                    NotPybindDerived.__new__(NotPybindDerived), tag.alias, 1
+                )
 
     for arg in (1, 2):
         with pytest.raises(TypeError) as excinfo:
             BrokenTF1(arg)
-        assert str(excinfo.value) == "__init__(self, ...) called with invalid `self` argument"
+        assert (
+            str(excinfo.value)
+            == "__init__(self, ...) called with invalid `self` argument"
+        )
 
     for arg in (1, 2, 3, 4):
         with pytest.raises(TypeError) as excinfo:
             BrokenTF6(arg)
-        assert str(excinfo.value) == "__init__(self, ...) called with invalid `self` argument"
+        assert (
+            str(excinfo.value)
+            == "__init__(self, ...) called with invalid `self` argument"
+        )
diff --git a/tests/test_gil_scoped.py b/tests/test_gil_scoped.py
index b2169d98b..0a1d62747 100644
--- a/tests/test_gil_scoped.py
+++ b/tests/test_gil_scoped.py
@@ -21,6 +21,7 @@ def _run_in_process(target, *args, **kwargs):
 
 def _python_to_cpp_to_python():
     """Calls different C++ functions that come back to Python."""
+
     class ExtendedVirtClass(m.VirtClass):
         def virtual_func(self):
             pass
@@ -74,7 +75,9 @@ def test_python_to_cpp_to_python_from_thread_multiple_sequential():
 
     It runs in a separate process to be able to stop and assert if it deadlocks.
     """
-    assert _run_in_process(_python_to_cpp_to_python_from_threads, 8, parallel=False) == 0
+    assert (
+        _run_in_process(_python_to_cpp_to_python_from_threads, 8, parallel=False) == 0
+    )
 
 
 # TODO: FIXME on macOS Python 3.9
diff --git a/tests/test_iostream.py b/tests/test_iostream.py
index 7ac4fcece..506db42ec 100644
--- a/tests/test_iostream.py
+++ b/tests/test_iostream.py
@@ -18,6 +18,7 @@ try:
     # Python 3.4
     from contextlib import redirect_stdout
 except ImportError:
+
     @contextmanager
     def redirect_stdout(target):
         original = sys.stdout
@@ -25,10 +26,12 @@ except ImportError:
         yield
         sys.stdout = original
 
+
 try:
     # Python 3.5
     from contextlib import redirect_stderr
 except ImportError:
+
     @contextmanager
     def redirect_stderr(target):
         original = sys.stderr
@@ -42,16 +45,16 @@ def test_captured(capsys):
     m.captured_output(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ''
+    assert stderr == ""
 
     m.captured_output_default(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ''
+    assert stderr == ""
 
     m.captured_err(msg)
     stdout, stderr = capsys.readouterr()
-    assert stdout == ''
+    assert stdout == ""
     assert stderr == msg
 
 
@@ -63,7 +66,7 @@ def test_captured_large_string(capsys):
     m.captured_output_default(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ''
+    assert stderr == ""
 
 
 def test_guard_capture(capsys):
@@ -71,7 +74,7 @@ def test_guard_capture(capsys):
     m.guard_output(msg)
     stdout, stderr = capsys.readouterr()
     assert stdout == msg
-    assert stderr == ''
+    assert stderr == ""
 
 
 def test_series_captured(capture):
@@ -88,7 +91,7 @@ def test_flush(capfd):
     with m.ostream_redirect():
         m.noisy_function(msg, flush=False)
         stdout, stderr = capfd.readouterr()
-        assert stdout == ''
+        assert stdout == ""
 
         m.noisy_function(msg2, flush=True)
         stdout, stderr = capfd.readouterr()
@@ -107,15 +110,15 @@ def test_not_captured(capfd):
         m.raw_output(msg)
     stdout, stderr = capfd.readouterr()
     assert stdout == msg
-    assert stderr == ''
-    assert stream.getvalue() == ''
+    assert stderr == ""
+    assert stream.getvalue() == ""
 
     stream = StringIO()
     with redirect_stdout(stream):
         m.captured_output(msg)
     stdout, stderr = capfd.readouterr()
-    assert stdout == ''
-    assert stderr == ''
+    assert stdout == ""
+    assert stderr == ""
     assert stream.getvalue() == msg
 
 
@@ -125,16 +128,16 @@ def test_err(capfd):
     with redirect_stderr(stream):
         m.raw_err(msg)
     stdout, stderr = capfd.readouterr()
-    assert stdout == ''
+    assert stdout == ""
     assert stderr == msg
-    assert stream.getvalue() == ''
+    assert stream.getvalue() == ""
 
     stream = StringIO()
     with redirect_stderr(stream):
         m.captured_err(msg)
     stdout, stderr = capfd.readouterr()
-    assert stdout == ''
-    assert stderr == ''
+    assert stdout == ""
+    assert stderr == ""
     assert stream.getvalue() == msg
 
 
@@ -146,8 +149,8 @@ def test_multi_captured(capfd):
         m.captured_output("c")
         m.raw_output("d")
     stdout, stderr = capfd.readouterr()
-    assert stdout == 'bd'
-    assert stream.getvalue() == 'ac'
+    assert stdout == "bd"
+    assert stream.getvalue() == "ac"
 
 
 def test_dual(capsys):
@@ -164,14 +167,14 @@ def test_redirect(capfd):
         m.raw_output(msg)
     stdout, stderr = capfd.readouterr()
     assert stdout == msg
-    assert stream.getvalue() == ''
+    assert stream.getvalue() == ""
 
     stream = StringIO()
     with redirect_stdout(stream):
         with m.ostream_redirect():
             m.raw_output(msg)
     stdout, stderr = capfd.readouterr()
-    assert stdout == ''
+    assert stdout == ""
     assert stream.getvalue() == msg
 
     stream = StringIO()
@@ -179,7 +182,7 @@ def test_redirect(capfd):
         m.raw_output(msg)
     stdout, stderr = capfd.readouterr()
     assert stdout == msg
-    assert stream.getvalue() == ''
+    assert stream.getvalue() == ""
 
 
 def test_redirect_err(capfd):
@@ -193,7 +196,7 @@ def test_redirect_err(capfd):
             m.raw_err(msg2)
     stdout, stderr = capfd.readouterr()
     assert stdout == msg
-    assert stderr == ''
+    assert stderr == ""
     assert stream.getvalue() == msg2
 
 
@@ -209,7 +212,7 @@ def test_redirect_both(capfd):
                 m.raw_output(msg)
                 m.raw_err(msg2)
     stdout, stderr = capfd.readouterr()
-    assert stdout == ''
-    assert stderr == ''
+    assert stdout == ""
+    assert stderr == ""
     assert stream.getvalue() == msg
     assert stream2.getvalue() == msg2
diff --git a/tests/test_kwargs_and_defaults.py b/tests/test_kwargs_and_defaults.py
index 2a81dbdc5..12fe705b4 100644
--- a/tests/test_kwargs_and_defaults.py
+++ b/tests/test_kwargs_and_defaults.py
@@ -15,11 +15,17 @@ def test_function_signatures(doc):
     assert doc(m.kw_func_udl) == "kw_func_udl(x: int, y: int = 300) -> str"
     assert doc(m.kw_func_udl_z) == "kw_func_udl_z(x: int, y: int = 0) -> str"
     assert doc(m.args_function) == "args_function(*args) -> tuple"
-    assert doc(m.args_kwargs_function) == "args_kwargs_function(*args, **kwargs) -> tuple"
-    assert doc(m.KWClass.foo0) == \
-        "foo0(self: m.kwargs_and_defaults.KWClass, arg0: int, arg1: float) -> None"
-    assert doc(m.KWClass.foo1) == \
-        "foo1(self: m.kwargs_and_defaults.KWClass, x: int, y: float) -> None"
+    assert (
+        doc(m.args_kwargs_function) == "args_kwargs_function(*args, **kwargs) -> tuple"
+    )
+    assert (
+        doc(m.KWClass.foo0)
+        == "foo0(self: m.kwargs_and_defaults.KWClass, arg0: int, arg1: float) -> None"
+    )
+    assert (
+        doc(m.KWClass.foo1)
+        == "foo1(self: m.kwargs_and_defaults.KWClass, x: int, y: float) -> None"
+    )
 
 
 def test_named_arguments(msg):
@@ -40,7 +46,9 @@ def test_named_arguments(msg):
         # noinspection PyArgumentList
         m.kw_func2(x=5, y=10, z=12)
     assert excinfo.match(
-        r'(?s)^kw_func2\(\): incompatible.*Invoked with: kwargs: ((x=5|y=10|z=12)(, |$))' + '{3}$')
+        r"(?s)^kw_func2\(\): incompatible.*Invoked with: kwargs: ((x=5|y=10|z=12)(, |$))"
+        + "{3}$"
+    )
 
     assert m.kw_func4() == "{13 17}"
     assert m.kw_func4(myList=[1, 2, 3]) == "{1 2 3}"
@@ -50,11 +58,11 @@ def test_named_arguments(msg):
 
 
 def test_arg_and_kwargs():
-    args = 'arg1_value', 'arg2_value', 3
+    args = "arg1_value", "arg2_value", 3
     assert m.args_function(*args) == args
 
-    args = 'a1', 'a2'
-    kwargs = dict(arg3='a3', arg4=4)
+    args = "a1", "a2"
+    kwargs = dict(arg3="a3", arg4=4)
     assert m.args_kwargs_function(*args, **kwargs) == (args, kwargs)
 
 
@@ -68,47 +76,71 @@ def test_mixed_args_and_kwargs(msg):
     assert mpa(1, 2.5) == (1, 2.5, ())
     with pytest.raises(TypeError) as excinfo:
         assert mpa(1)
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         mixed_plus_args(): incompatible function arguments. The following argument types are supported:
             1. (arg0: int, arg1: float, *args) -> tuple
 
         Invoked with: 1
     """  # noqa: E501 line too long
+    )
     with pytest.raises(TypeError) as excinfo:
         assert mpa()
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         mixed_plus_args(): incompatible function arguments. The following argument types are supported:
             1. (arg0: int, arg1: float, *args) -> tuple
 
         Invoked with:
     """  # noqa: E501 line too long
+    )
 
-    assert mpk(-2, 3.5, pi=3.14159, e=2.71828) == (-2, 3.5, {'e': 2.71828, 'pi': 3.14159})
+    assert mpk(-2, 3.5, pi=3.14159, e=2.71828) == (
+        -2,
+        3.5,
+        {"e": 2.71828, "pi": 3.14159},
+    )
     assert mpak(7, 7.7, 7.77, 7.777, 7.7777, minusseven=-7) == (
-        7, 7.7, (7.77, 7.777, 7.7777), {'minusseven': -7})
+        7,
+        7.7,
+        (7.77, 7.777, 7.7777),
+        {"minusseven": -7},
+    )
     assert mpakd() == (1, 3.14159, (), {})
     assert mpakd(3) == (3, 3.14159, (), {})
     assert mpakd(j=2.71828) == (1, 2.71828, (), {})
-    assert mpakd(k=42) == (1, 3.14159, (), {'k': 42})
+    assert mpakd(k=42) == (1, 3.14159, (), {"k": 42})
     assert mpakd(1, 1, 2, 3, 5, 8, then=13, followedby=21) == (
-        1, 1, (2, 3, 5, 8), {'then': 13, 'followedby': 21})
+        1,
+        1,
+        (2, 3, 5, 8),
+        {"then": 13, "followedby": 21},
+    )
     # Arguments specified both positionally and via kwargs should fail:
     with pytest.raises(TypeError) as excinfo:
         assert mpakd(1, i=1)
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         mixed_plus_args_kwargs_defaults(): incompatible function arguments. The following argument types are supported:
             1. (i: int = 1, j: float = 3.14159, *args, **kwargs) -> tuple
 
         Invoked with: 1; kwargs: i=1
     """  # noqa: E501 line too long
+    )
     with pytest.raises(TypeError) as excinfo:
         assert mpakd(1, 2, j=1)
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         mixed_plus_args_kwargs_defaults(): incompatible function arguments. The following argument types are supported:
             1. (i: int = 1, j: float = 3.14159, *args, **kwargs) -> tuple
 
         Invoked with: 1, 2; kwargs: j=1
     """  # noqa: E501 line too long
+    )
 
 
 def test_keyword_only_args(msg):
@@ -134,9 +166,9 @@ def test_keyword_only_args(msg):
     assert m.kw_only_mixed(j=2, i=3) == (3, 2)
     assert m.kw_only_mixed(i=2, j=3) == (2, 3)
 
-    assert m.kw_only_plus_more(4, 5, k=6, extra=7) == (4, 5, 6, {'extra': 7})
-    assert m.kw_only_plus_more(3, k=5, j=4, extra=6) == (3, 4, 5, {'extra': 6})
-    assert m.kw_only_plus_more(2, k=3, extra=4) == (2, -1, 3, {'extra': 4})
+    assert m.kw_only_plus_more(4, 5, k=6, extra=7) == (4, 5, 6, {"extra": 7})
+    assert m.kw_only_plus_more(3, k=5, j=4, extra=6) == (3, 4, 5, {"extra": 6})
+    assert m.kw_only_plus_more(2, k=3, extra=4) == (2, -1, 3, {"extra": 4})
 
     with pytest.raises(TypeError) as excinfo:
         assert m.kw_only_mixed(i=1) == (1,)
@@ -144,9 +176,12 @@ def test_keyword_only_args(msg):
 
     with pytest.raises(RuntimeError) as excinfo:
         m.register_invalid_kw_only(m)
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         arg(): cannot specify an unnamed argument after an kw_only() annotation
     """
+    )
 
 
 def test_positional_only_args(msg):
@@ -194,7 +229,10 @@ def test_signatures():
     assert "kw_only_mixed(i: int, *, j: int) -> tuple\n" == m.kw_only_mixed.__doc__
     assert "pos_only_all(i: int, j: int, /) -> tuple\n" == m.pos_only_all.__doc__
     assert "pos_only_mix(i: int, /, j: int) -> tuple\n" == m.pos_only_mix.__doc__
-    assert "pos_kw_only_mix(i: int, /, j: int, *, k: int) -> tuple\n" == m.pos_kw_only_mix.__doc__
+    assert (
+        "pos_kw_only_mix(i: int, /, j: int, *, k: int) -> tuple\n"
+        == m.pos_kw_only_mix.__doc__
+    )
 
 
 @pytest.mark.xfail("env.PYPY and env.PY2", reason="PyPy2 doesn't double count")
@@ -219,11 +257,18 @@ def test_args_refcount():
     assert m.args_function(-1, myval) == (-1, myval)
     assert refcount(myval) == expected
 
-    assert m.mixed_plus_args_kwargs(5, 6.0, myval, a=myval) == (5, 6.0, (myval,), {"a": myval})
+    assert m.mixed_plus_args_kwargs(5, 6.0, myval, a=myval) == (
+        5,
+        6.0,
+        (myval,),
+        {"a": myval},
+    )
     assert refcount(myval) == expected
 
-    assert m.args_kwargs_function(7, 8, myval, a=1, b=myval) == \
-        ((7, 8, myval), {"a": 1, "b": myval})
+    assert m.args_kwargs_function(7, 8, myval, a=1, b=myval) == (
+        (7, 8, myval),
+        {"a": 1, "b": myval},
+    )
     assert refcount(myval) == expected
 
     exp3 = refcount(myval, myval, myval)
diff --git a/tests/test_local_bindings.py b/tests/test_local_bindings.py
index ebc4873e2..d23c46752 100644
--- a/tests/test_local_bindings.py
+++ b/tests/test_local_bindings.py
@@ -36,8 +36,8 @@ def test_local_bindings():
     assert i2.get() == 11
     assert i2.get2() == 12
 
-    assert not hasattr(i1, 'get2')
-    assert not hasattr(i2, 'get3')
+    assert not hasattr(i1, "get2")
+    assert not hasattr(i2, "get3")
 
     # Loading within the local module
     assert m.local_value(i1) == 5
@@ -55,7 +55,9 @@ def test_nonlocal_failure():
 
     with pytest.raises(RuntimeError) as excinfo:
         cm.register_nonlocal()
-    assert str(excinfo.value) == 'generic_type: type "NonLocalType" is already registered!'
+    assert (
+        str(excinfo.value) == 'generic_type: type "NonLocalType" is already registered!'
+    )
 
 
 def test_duplicate_local():
@@ -63,9 +65,12 @@ def test_duplicate_local():
     with pytest.raises(RuntimeError) as excinfo:
         m.register_local_external()
     import pybind11_tests
+
     assert str(excinfo.value) == (
         'generic_type: type "LocalExternal" is already registered!'
-        if hasattr(pybind11_tests, 'class_') else 'test_class not enabled')
+        if hasattr(pybind11_tests, "class_")
+        else "test_class not enabled"
+    )
 
 
 def test_stl_bind_local():
@@ -98,8 +103,8 @@ def test_stl_bind_local():
     d1["b"] = v1[1]
     d2["c"] = v2[0]
     d2["d"] = v2[1]
-    assert {i: d1[i].get() for i in d1} == {'a': 0, 'b': 1}
-    assert {i: d2[i].get() for i in d2} == {'c': 2, 'd': 3}
+    assert {i: d1[i].get() for i in d1} == {"a": 0, "b": 1}
+    assert {i: d2[i].get() for i in d2} == {"c": 2, "d": 3}
 
 
 def test_stl_bind_global():
@@ -107,15 +112,21 @@ def test_stl_bind_global():
 
     with pytest.raises(RuntimeError) as excinfo:
         cm.register_nonlocal_map()
-    assert str(excinfo.value) == 'generic_type: type "NonLocalMap" is already registered!'
+    assert (
+        str(excinfo.value) == 'generic_type: type "NonLocalMap" is already registered!'
+    )
 
     with pytest.raises(RuntimeError) as excinfo:
         cm.register_nonlocal_vec()
-    assert str(excinfo.value) == 'generic_type: type "NonLocalVec" is already registered!'
+    assert (
+        str(excinfo.value) == 'generic_type: type "NonLocalVec" is already registered!'
+    )
 
     with pytest.raises(RuntimeError) as excinfo:
         cm.register_nonlocal_map2()
-    assert str(excinfo.value) == 'generic_type: type "NonLocalMap2" is already registered!'
+    assert (
+        str(excinfo.value) == 'generic_type: type "NonLocalMap2" is already registered!'
+    )
 
 
 def test_mixed_local_global():
@@ -123,6 +134,7 @@ def test_mixed_local_global():
     type can be registered even if the type is already registered globally.  With the module,
     casting will go to the local type; outside the module casting goes to the global type."""
     import pybind11_cross_module_tests as cm
+
     m.register_mixed_global()
     m.register_mixed_local()
 
@@ -145,13 +157,26 @@ def test_mixed_local_global():
     a.append(cm.get_mixed_gl(11))
     a.append(cm.get_mixed_lg(12))
 
-    assert [x.get() for x in a] == \
-        [101, 1002, 103, 1004, 105, 1006, 207, 2008, 109, 1010, 211, 2012]
+    assert [x.get() for x in a] == [
+        101,
+        1002,
+        103,
+        1004,
+        105,
+        1006,
+        207,
+        2008,
+        109,
+        1010,
+        211,
+        2012,
+    ]
 
 
 def test_internal_locals_differ():
     """Makes sure the internal local type map differs across the two modules"""
     import pybind11_cross_module_tests as cm
+
     assert m.local_cpp_types_addr() != cm.local_cpp_types_addr()
 
 
@@ -169,12 +194,15 @@ def test_stl_caster_vs_stl_bind(msg):
     assert m.load_vector_via_caster(v2) == 6
     with pytest.raises(TypeError) as excinfo:
         cm.load_vector_via_binding(v2) == 6
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
     load_vector_via_binding(): incompatible function arguments. The following argument types are supported:
         1. (arg0: pybind11_cross_module_tests.VectorInt) -> int
 
     Invoked with: [1, 2, 3]
     """  # noqa: E501 line too long
+    )
 
 
 def test_cross_module_calls():
diff --git a/tests/test_methods_and_attributes.py b/tests/test_methods_and_attributes.py
index d5793296b..3e0e6cf05 100644
--- a/tests/test_methods_and_attributes.py
+++ b/tests/test_methods_and_attributes.py
@@ -40,17 +40,17 @@ def test_methods_and_attributes():
     assert instance1.overloaded(0) == "(int)"
     assert instance1.overloaded(1, 1.0) == "(int, float)"
     assert instance1.overloaded(2.0, 2) == "(float, int)"
-    assert instance1.overloaded(3,   3) == "(int, int)"
-    assert instance1.overloaded(4., 4.) == "(float, float)"
+    assert instance1.overloaded(3, 3) == "(int, int)"
+    assert instance1.overloaded(4.0, 4.0) == "(float, float)"
     assert instance1.overloaded_const(-3) == "(int) const"
     assert instance1.overloaded_const(5, 5.0) == "(int, float) const"
     assert instance1.overloaded_const(6.0, 6) == "(float, int) const"
-    assert instance1.overloaded_const(7,   7) == "(int, int) const"
-    assert instance1.overloaded_const(8., 8.) == "(float, float) const"
+    assert instance1.overloaded_const(7, 7) == "(int, int) const"
+    assert instance1.overloaded_const(8.0, 8.0) == "(float, float) const"
     assert instance1.overloaded_float(1, 1) == "(float, float)"
-    assert instance1.overloaded_float(1, 1.) == "(float, float)"
-    assert instance1.overloaded_float(1., 1) == "(float, float)"
-    assert instance1.overloaded_float(1., 1.) == "(float, float)"
+    assert instance1.overloaded_float(1, 1.0) == "(float, float)"
+    assert instance1.overloaded_float(1.0, 1) == "(float, float)"
+    assert instance1.overloaded_float(1.0, 1.0) == "(float, float)"
 
     assert instance1.value == 320
     instance1.value = 100
@@ -193,7 +193,10 @@ def test_metaclass_override():
     assert type(m.MetaclassOverride).__name__ == "type"
 
     assert m.MetaclassOverride.readonly == 1
-    assert type(m.MetaclassOverride.__dict__["readonly"]).__name__ == "pybind11_static_property"
+    assert (
+        type(m.MetaclassOverride.__dict__["readonly"]).__name__
+        == "pybind11_static_property"
+    )
 
     # Regular `type` replaces the property instead of calling `__set__()`
     m.MetaclassOverride.readonly = 2
@@ -206,22 +209,26 @@ def test_no_mixed_overloads():
 
     with pytest.raises(RuntimeError) as excinfo:
         m.ExampleMandA.add_mixed_overloads1()
-    assert (str(excinfo.value) ==
-            "overloading a method with both static and instance methods is not supported; " +
-            ("compile in debug mode for more details" if not debug_enabled else
-             "error while attempting to bind static method ExampleMandA.overload_mixed1"
-             "(arg0: float) -> str")
-            )
+    assert str(
+        excinfo.value
+    ) == "overloading a method with both static and instance methods is not supported; " + (
+        "compile in debug mode for more details"
+        if not debug_enabled
+        else "error while attempting to bind static method ExampleMandA.overload_mixed1"
+        "(arg0: float) -> str"
+    )
 
     with pytest.raises(RuntimeError) as excinfo:
         m.ExampleMandA.add_mixed_overloads2()
-    assert (str(excinfo.value) ==
-            "overloading a method with both static and instance methods is not supported; " +
-            ("compile in debug mode for more details" if not debug_enabled else
-             "error while attempting to bind instance method ExampleMandA.overload_mixed2"
-             "(self: pybind11_tests.methods_and_attributes.ExampleMandA, arg0: int, arg1: int)"
-             " -> str")
-            )
+    assert str(
+        excinfo.value
+    ) == "overloading a method with both static and instance methods is not supported; " + (
+        "compile in debug mode for more details"
+        if not debug_enabled
+        else "error while attempting to bind instance method ExampleMandA.overload_mixed2"
+        "(self: pybind11_tests.methods_and_attributes.ExampleMandA, arg0: int, arg1: int)"
+        " -> str"
+    )
 
 
 @pytest.mark.parametrize("access", ["ro", "rw", "static_ro", "static_rw"])
@@ -333,8 +340,8 @@ def test_bad_arg_default(msg):
     assert msg(excinfo.value) == (
         "arg(): could not convert default argument 'a: UnregisteredType' in function "
         "'should_fail' into a Python object (type not registered yet?)"
-        if debug_enabled else
-        "arg(): could not convert default argument into a Python object (type not registered "
+        if debug_enabled
+        else "arg(): could not convert default argument into a Python object (type not registered "
         "yet?). Compile in debug mode for more information."
     )
 
@@ -343,8 +350,8 @@ def test_bad_arg_default(msg):
     assert msg(excinfo.value) == (
         "arg(): could not convert default argument 'UnregisteredType' in function "
         "'should_fail' into a Python object (type not registered yet?)"
-        if debug_enabled else
-        "arg(): could not convert default argument into a Python object (type not registered "
+        if debug_enabled
+        else "arg(): could not convert default argument into a Python object (type not registered "
         "yet?). Compile in debug mode for more information."
     )
 
@@ -381,12 +388,15 @@ def test_accepts_none(msg):
     # The first one still raises because you can't pass None as a lvalue reference arg:
     with pytest.raises(TypeError) as excinfo:
         assert m.ok_none1(None) == -1
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         ok_none1(): incompatible function arguments. The following argument types are supported:
             1. (arg0: m.methods_and_attributes.NoneTester) -> int
 
         Invoked with: None
     """
+    )
 
     # The rest take the argument as pointer or holder, and accept None:
     assert m.ok_none2(None) == -1
@@ -402,13 +412,16 @@ def test_str_issue(msg):
 
     with pytest.raises(TypeError) as excinfo:
         str(m.StrIssue("no", "such", "constructor"))
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         __init__(): incompatible constructor arguments. The following argument types are supported:
             1. m.methods_and_attributes.StrIssue(arg0: int)
             2. m.methods_and_attributes.StrIssue()
 
         Invoked with: 'no', 'such', 'constructor'
     """
+    )
 
 
 def test_unregistered_base_implementations():
@@ -441,7 +454,7 @@ def test_ref_qualified():
 
 
 def test_overload_ordering():
-    'Check to see if the normal overload order (first defined) and prepend overload order works'
+    "Check to see if the normal overload order (first defined) and prepend overload order works"
     assert m.overload_order("string") == 1
     assert m.overload_order(0) == 4
 
@@ -449,8 +462,14 @@ def test_overload_ordering():
     uni_name = type(u"").__name__
 
     assert "1. overload_order(arg0: int) -> int" in m.overload_order.__doc__
-    assert "2. overload_order(arg0: {}) -> int".format(uni_name) in m.overload_order.__doc__
-    assert "3. overload_order(arg0: {}) -> int".format(uni_name) in m.overload_order.__doc__
+    assert (
+        "2. overload_order(arg0: {}) -> int".format(uni_name)
+        in m.overload_order.__doc__
+    )
+    assert (
+        "3. overload_order(arg0: {}) -> int".format(uni_name)
+        in m.overload_order.__doc__
+    )
     assert "4. overload_order(arg0: int) -> int" in m.overload_order.__doc__
 
     with pytest.raises(TypeError) as err:
diff --git a/tests/test_modules.py b/tests/test_modules.py
index 7e2100524..5630ccf9b 100644
--- a/tests/test_modules.py
+++ b/tests/test_modules.py
@@ -6,9 +6,13 @@ from pybind11_tests import ConstructorStats
 
 def test_nested_modules():
     import pybind11_tests
+
     assert pybind11_tests.__name__ == "pybind11_tests"
     assert pybind11_tests.modules.__name__ == "pybind11_tests.modules"
-    assert pybind11_tests.modules.subsubmodule.__name__ == "pybind11_tests.modules.subsubmodule"
+    assert (
+        pybind11_tests.modules.subsubmodule.__name__
+        == "pybind11_tests.modules.subsubmodule"
+    )
     assert m.__name__ == "pybind11_tests.modules"
     assert ms.__name__ == "pybind11_tests.modules.subsubmodule"
 
@@ -35,7 +39,7 @@ def test_reference_internal():
     del b
     assert astats.alive() == 0
     assert bstats.alive() == 0
-    assert astats.values() == ['1', '2', '42', '43']
+    assert astats.values() == ["1", "2", "42", "43"]
     assert bstats.values() == []
     assert astats.default_constructions == 0
     assert bstats.default_constructions == 1
@@ -54,7 +58,7 @@ def test_importing():
     from collections import OrderedDict
 
     assert OD is OrderedDict
-    assert str(OD([(1, 'a'), (2, 'b')])) == "OrderedDict([(1, 'a'), (2, 'b')])"
+    assert str(OD([(1, "a"), (2, "b")])) == "OrderedDict([(1, 'a'), (2, 'b')])"
 
 
 def test_pydoc():
diff --git a/tests/test_multiple_inheritance.py b/tests/test_multiple_inheritance.py
index 7a0259d21..e6a7f9762 100644
--- a/tests/test_multiple_inheritance.py
+++ b/tests/test_multiple_inheritance.py
@@ -57,7 +57,6 @@ def test_multiple_inheritance_mix2():
 @pytest.mark.skipif("env.PYPY and env.PY2")
 @pytest.mark.xfail("env.PYPY and not env.PY2")
 def test_multiple_inheritance_python():
-
     class MI1(m.Base1, m.Base2):
         def __init__(self, i, j):
             m.Base1.__init__(self, i)
@@ -163,7 +162,6 @@ def test_multiple_inheritance_python():
 
 
 def test_multiple_inheritance_python_many_bases():
-
     class MIMany14(m.BaseN1, m.BaseN2, m.BaseN3, m.BaseN4):
         def __init__(self):
             m.BaseN1.__init__(self, 1)
@@ -178,8 +176,16 @@ def test_multiple_inheritance_python_many_bases():
             m.BaseN7.__init__(self, 7)
             m.BaseN8.__init__(self, 8)
 
-    class MIMany916(m.BaseN9, m.BaseN10, m.BaseN11, m.BaseN12, m.BaseN13, m.BaseN14, m.BaseN15,
-                    m.BaseN16):
+    class MIMany916(
+        m.BaseN9,
+        m.BaseN10,
+        m.BaseN11,
+        m.BaseN12,
+        m.BaseN13,
+        m.BaseN14,
+        m.BaseN15,
+        m.BaseN16,
+    ):
         def __init__(self):
             m.BaseN9.__init__(self, 9)
             m.BaseN10.__init__(self, 10)
@@ -225,7 +231,6 @@ def test_multiple_inheritance_python_many_bases():
 
 
 def test_multiple_inheritance_virtbase():
-
     class MITypePy(m.Base12a):
         def __init__(self, i, j):
             m.Base12a.__init__(self, i, j)
@@ -238,7 +243,7 @@ def test_multiple_inheritance_virtbase():
 
 def test_mi_static_properties():
     """Mixing bases with and without static properties should be possible
-     and the result should be independent of base definition order"""
+    and the result should be independent of base definition order"""
 
     for d in (m.VanillaStaticMix1(), m.VanillaStaticMix2()):
         assert d.vanilla() == "Vanilla"
diff --git a/tests/test_numpy_array.py b/tests/test_numpy_array.py
index e3e7c5f57..02f3ecfc0 100644
--- a/tests/test_numpy_array.py
+++ b/tests/test_numpy_array.py
@@ -19,33 +19,36 @@ def test_dtypes():
         print(check)
         assert check.numpy == check.pybind11, check
         if check.numpy.num != check.pybind11.num:
-            print("NOTE: typenum mismatch for {}: {} != {}".format(
-                check, check.numpy.num, check.pybind11.num))
+            print(
+                "NOTE: typenum mismatch for {}: {} != {}".format(
+                    check, check.numpy.num, check.pybind11.num
+                )
+            )
 
 
-@pytest.fixture(scope='function')
+@pytest.fixture(scope="function")
 def arr():
-    return np.array([[1, 2, 3], [4, 5, 6]], '=u2')
+    return np.array([[1, 2, 3], [4, 5, 6]], "=u2")
 
 
 def test_array_attributes():
-    a = np.array(0, 'f8')
+    a = np.array(0, "f8")
     assert m.ndim(a) == 0
     assert all(m.shape(a) == [])
     assert all(m.strides(a) == [])
     with pytest.raises(IndexError) as excinfo:
         m.shape(a, 0)
-    assert str(excinfo.value) == 'invalid axis: 0 (ndim = 0)'
+    assert str(excinfo.value) == "invalid axis: 0 (ndim = 0)"
     with pytest.raises(IndexError) as excinfo:
         m.strides(a, 0)
-    assert str(excinfo.value) == 'invalid axis: 0 (ndim = 0)'
+    assert str(excinfo.value) == "invalid axis: 0 (ndim = 0)"
     assert m.writeable(a)
     assert m.size(a) == 1
     assert m.itemsize(a) == 8
     assert m.nbytes(a) == 8
     assert m.owndata(a)
 
-    a = np.array([[1, 2, 3], [4, 5, 6]], 'u2').view()
+    a = np.array([[1, 2, 3], [4, 5, 6]], "u2").view()
     a.flags.writeable = False
     assert m.ndim(a) == 2
     assert all(m.shape(a) == [2, 3])
@@ -56,10 +59,10 @@ def test_array_attributes():
     assert m.strides(a, 1) == 2
     with pytest.raises(IndexError) as excinfo:
         m.shape(a, 2)
-    assert str(excinfo.value) == 'invalid axis: 2 (ndim = 2)'
+    assert str(excinfo.value) == "invalid axis: 2 (ndim = 2)"
     with pytest.raises(IndexError) as excinfo:
         m.strides(a, 2)
-    assert str(excinfo.value) == 'invalid axis: 2 (ndim = 2)'
+    assert str(excinfo.value) == "invalid axis: 2 (ndim = 2)"
     assert not m.writeable(a)
     assert m.size(a) == 6
     assert m.itemsize(a) == 2
@@ -67,7 +70,9 @@ def test_array_attributes():
     assert not m.owndata(a)
 
 
-@pytest.mark.parametrize('args, ret', [([], 0), ([0], 0), ([1], 3), ([0, 1], 1), ([1, 2], 5)])
+@pytest.mark.parametrize(
+    "args, ret", [([], 0), ([0], 0), ([1], 3), ([0, 1], 1), ([1, 2], 5)]
+)
 def test_index_offset(arr, args, ret):
     assert m.index_at(arr, *args) == ret
     assert m.index_at_t(arr, *args) == ret
@@ -76,31 +81,46 @@ def test_index_offset(arr, args, ret):
 
 
 def test_dim_check_fail(arr):
-    for func in (m.index_at, m.index_at_t, m.offset_at, m.offset_at_t, m.data, m.data_t,
-                 m.mutate_data, m.mutate_data_t):
+    for func in (
+        m.index_at,
+        m.index_at_t,
+        m.offset_at,
+        m.offset_at_t,
+        m.data,
+        m.data_t,
+        m.mutate_data,
+        m.mutate_data_t,
+    ):
         with pytest.raises(IndexError) as excinfo:
             func(arr, 1, 2, 3)
-        assert str(excinfo.value) == 'too many indices for an array: 3 (ndim = 2)'
+        assert str(excinfo.value) == "too many indices for an array: 3 (ndim = 2)"
 
 
-@pytest.mark.parametrize('args, ret',
-                         [([], [1, 2, 3, 4, 5, 6]),
-                          ([1], [4, 5, 6]),
-                          ([0, 1], [2, 3, 4, 5, 6]),
-                          ([1, 2], [6])])
+@pytest.mark.parametrize(
+    "args, ret",
+    [
+        ([], [1, 2, 3, 4, 5, 6]),
+        ([1], [4, 5, 6]),
+        ([0, 1], [2, 3, 4, 5, 6]),
+        ([1, 2], [6]),
+    ],
+)
 def test_data(arr, args, ret):
     from sys import byteorder
+
     assert all(m.data_t(arr, *args) == ret)
-    assert all(m.data(arr, *args)[(0 if byteorder == 'little' else 1)::2] == ret)
-    assert all(m.data(arr, *args)[(1 if byteorder == 'little' else 0)::2] == 0)
+    assert all(m.data(arr, *args)[(0 if byteorder == "little" else 1) :: 2] == ret)
+    assert all(m.data(arr, *args)[(1 if byteorder == "little" else 0) :: 2] == 0)
 
 
-@pytest.mark.parametrize('dim', [0, 1, 3])
+@pytest.mark.parametrize("dim", [0, 1, 3])
 def test_at_fail(arr, dim):
     for func in m.at_t, m.mutate_at_t:
         with pytest.raises(IndexError) as excinfo:
             func(arr, *([0] * dim))
-        assert str(excinfo.value) == 'index dimension mismatch: {} (ndim = 2)'.format(dim)
+        assert str(excinfo.value) == "index dimension mismatch: {} (ndim = 2)".format(
+            dim
+        )
 
 
 def test_at(arr):
@@ -113,10 +133,14 @@ def test_at(arr):
 
 def test_mutate_readonly(arr):
     arr.flags.writeable = False
-    for func, args in (m.mutate_data, ()), (m.mutate_data_t, ()), (m.mutate_at_t, (0, 0)):
+    for func, args in (
+        (m.mutate_data, ()),
+        (m.mutate_data_t, ()),
+        (m.mutate_at_t, (0, 0)),
+    ):
         with pytest.raises(ValueError) as excinfo:
             func(arr, *args)
-        assert str(excinfo.value) == 'array is not writeable'
+        assert str(excinfo.value) == "array is not writeable"
 
 
 def test_mutate_data(arr):
@@ -134,14 +158,22 @@ def test_mutate_data(arr):
 
 
 def test_bounds_check(arr):
-    for func in (m.index_at, m.index_at_t, m.data, m.data_t,
-                 m.mutate_data, m.mutate_data_t, m.at_t, m.mutate_at_t):
+    for func in (
+        m.index_at,
+        m.index_at_t,
+        m.data,
+        m.data_t,
+        m.mutate_data,
+        m.mutate_data_t,
+        m.at_t,
+        m.mutate_at_t,
+    ):
         with pytest.raises(IndexError) as excinfo:
             func(arr, 2, 0)
-        assert str(excinfo.value) == 'index 2 is out of bounds for axis 0 with size 2'
+        assert str(excinfo.value) == "index 2 is out of bounds for axis 0 with size 2"
         with pytest.raises(IndexError) as excinfo:
             func(arr, 0, 4)
-        assert str(excinfo.value) == 'index 4 is out of bounds for axis 1 with size 3'
+        assert str(excinfo.value) == "index 4 is out of bounds for axis 1 with size 3"
 
 
 def test_make_c_f_array():
@@ -163,10 +195,11 @@ def test_make_empty_shaped_array():
 def test_wrap():
     def assert_references(a, b, base=None):
         from distutils.version import LooseVersion
+
         if base is None:
             base = a
         assert a is not b
-        assert a.__array_interface__['data'][0] == b.__array_interface__['data'][0]
+        assert a.__array_interface__["data"][0] == b.__array_interface__["data"][0]
         assert a.shape == b.shape
         assert a.strides == b.strides
         assert a.flags.c_contiguous == b.flags.c_contiguous
@@ -189,12 +222,12 @@ def test_wrap():
     a2 = m.wrap(a1)
     assert_references(a1, a2)
 
-    a1 = np.array([[1, 2], [3, 4]], dtype=np.float32, order='F')
+    a1 = np.array([[1, 2], [3, 4]], dtype=np.float32, order="F")
     assert a1.flags.owndata and a1.base is None
     a2 = m.wrap(a1)
     assert_references(a1, a2)
 
-    a1 = np.array([[1, 2], [3, 4]], dtype=np.float32, order='C')
+    a1 = np.array([[1, 2], [3, 4]], dtype=np.float32, order="C")
     a1.flags.writeable = False
     a2 = m.wrap(a1)
     assert_references(a1, a2)
@@ -224,11 +257,14 @@ def test_numpy_view(capture):
         assert np.all(ac_view_1 == np.array([1, 2], dtype=np.int32))
         del ac
         pytest.gc_collect()
-    assert capture == """
+    assert (
+        capture
+        == """
         ArrayClass()
         ArrayClass::numpy_view()
         ArrayClass::numpy_view()
     """
+    )
     ac_view_1[0] = 4
     ac_view_1[1] = 3
     assert ac_view_2[0] == 4
@@ -238,9 +274,12 @@ def test_numpy_view(capture):
         del ac_view_2
         pytest.gc_collect()
         pytest.gc_collect()
-    assert capture == """
+    assert (
+        capture
+        == """
         ~ArrayClass()
     """
+    )
 
 
 def test_cast_numpy_int64_to_uint64():
@@ -271,20 +310,22 @@ def test_constructors():
 
 def test_overload_resolution(msg):
     # Exact overload matches:
-    assert m.overloaded(np.array([1], dtype='float64')) == 'double'
-    assert m.overloaded(np.array([1], dtype='float32')) == 'float'
-    assert m.overloaded(np.array([1], dtype='ushort')) == 'unsigned short'
-    assert m.overloaded(np.array([1], dtype='intc')) == 'int'
-    assert m.overloaded(np.array([1], dtype='longlong')) == 'long long'
-    assert m.overloaded(np.array([1], dtype='complex')) == 'double complex'
-    assert m.overloaded(np.array([1], dtype='csingle')) == 'float complex'
+    assert m.overloaded(np.array([1], dtype="float64")) == "double"
+    assert m.overloaded(np.array([1], dtype="float32")) == "float"
+    assert m.overloaded(np.array([1], dtype="ushort")) == "unsigned short"
+    assert m.overloaded(np.array([1], dtype="intc")) == "int"
+    assert m.overloaded(np.array([1], dtype="longlong")) == "long long"
+    assert m.overloaded(np.array([1], dtype="complex")) == "double complex"
+    assert m.overloaded(np.array([1], dtype="csingle")) == "float complex"
 
     # No exact match, should call first convertible version:
-    assert m.overloaded(np.array([1], dtype='uint8')) == 'double'
+    assert m.overloaded(np.array([1], dtype="uint8")) == "double"
 
     with pytest.raises(TypeError) as excinfo:
         m.overloaded("not an array")
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         overloaded(): incompatible function arguments. The following argument types are supported:
             1. (arg0: numpy.ndarray[numpy.float64]) -> str
             2. (arg0: numpy.ndarray[numpy.float32]) -> str
@@ -296,15 +337,16 @@ def test_overload_resolution(msg):
 
         Invoked with: 'not an array'
     """
+    )
 
-    assert m.overloaded2(np.array([1], dtype='float64')) == 'double'
-    assert m.overloaded2(np.array([1], dtype='float32')) == 'float'
-    assert m.overloaded2(np.array([1], dtype='complex64')) == 'float complex'
-    assert m.overloaded2(np.array([1], dtype='complex128')) == 'double complex'
-    assert m.overloaded2(np.array([1], dtype='float32')) == 'float'
+    assert m.overloaded2(np.array([1], dtype="float64")) == "double"
+    assert m.overloaded2(np.array([1], dtype="float32")) == "float"
+    assert m.overloaded2(np.array([1], dtype="complex64")) == "float complex"
+    assert m.overloaded2(np.array([1], dtype="complex128")) == "double complex"
+    assert m.overloaded2(np.array([1], dtype="float32")) == "float"
 
-    assert m.overloaded3(np.array([1], dtype='float64')) == 'double'
-    assert m.overloaded3(np.array([1], dtype='intc')) == 'int'
+    assert m.overloaded3(np.array([1], dtype="float64")) == "double"
+    assert m.overloaded3(np.array([1], dtype="intc")) == "int"
     expected_exc = """
         overloaded3(): incompatible function arguments. The following argument types are supported:
             1. (arg0: numpy.ndarray[numpy.int32]) -> str
@@ -313,47 +355,49 @@ def test_overload_resolution(msg):
         Invoked with: """
 
     with pytest.raises(TypeError) as excinfo:
-        m.overloaded3(np.array([1], dtype='uintc'))
-    assert msg(excinfo.value) == expected_exc + repr(np.array([1], dtype='uint32'))
+        m.overloaded3(np.array([1], dtype="uintc"))
+    assert msg(excinfo.value) == expected_exc + repr(np.array([1], dtype="uint32"))
     with pytest.raises(TypeError) as excinfo:
-        m.overloaded3(np.array([1], dtype='float32'))
-    assert msg(excinfo.value) == expected_exc + repr(np.array([1.], dtype='float32'))
+        m.overloaded3(np.array([1], dtype="float32"))
+    assert msg(excinfo.value) == expected_exc + repr(np.array([1.0], dtype="float32"))
     with pytest.raises(TypeError) as excinfo:
-        m.overloaded3(np.array([1], dtype='complex'))
-    assert msg(excinfo.value) == expected_exc + repr(np.array([1. + 0.j]))
+        m.overloaded3(np.array([1], dtype="complex"))
+    assert msg(excinfo.value) == expected_exc + repr(np.array([1.0 + 0.0j]))
 
     # Exact matches:
-    assert m.overloaded4(np.array([1], dtype='double')) == 'double'
-    assert m.overloaded4(np.array([1], dtype='longlong')) == 'long long'
+    assert m.overloaded4(np.array([1], dtype="double")) == "double"
+    assert m.overloaded4(np.array([1], dtype="longlong")) == "long long"
     # Non-exact matches requiring conversion.  Since float to integer isn't a
     # save conversion, it should go to the double overload, but short can go to
     # either (and so should end up on the first-registered, the long long).
-    assert m.overloaded4(np.array([1], dtype='float32')) == 'double'
-    assert m.overloaded4(np.array([1], dtype='short')) == 'long long'
+    assert m.overloaded4(np.array([1], dtype="float32")) == "double"
+    assert m.overloaded4(np.array([1], dtype="short")) == "long long"
 
-    assert m.overloaded5(np.array([1], dtype='double')) == 'double'
-    assert m.overloaded5(np.array([1], dtype='uintc')) == 'unsigned int'
-    assert m.overloaded5(np.array([1], dtype='float32')) == 'unsigned int'
+    assert m.overloaded5(np.array([1], dtype="double")) == "double"
+    assert m.overloaded5(np.array([1], dtype="uintc")) == "unsigned int"
+    assert m.overloaded5(np.array([1], dtype="float32")) == "unsigned int"
 
 
 def test_greedy_string_overload():
     """Tests fix for #685 - ndarray shouldn't go to std::string overload"""
 
     assert m.issue685("abc") == "string"
-    assert m.issue685(np.array([97, 98, 99], dtype='b')) == "array"
+    assert m.issue685(np.array([97, 98, 99], dtype="b")) == "array"
     assert m.issue685(123) == "other"
 
 
 def test_array_unchecked_fixed_dims(msg):
-    z1 = np.array([[1, 2], [3, 4]], dtype='float64')
+    z1 = np.array([[1, 2], [3, 4]], dtype="float64")
     m.proxy_add2(z1, 10)
     assert np.all(z1 == [[11, 12], [13, 14]])
 
     with pytest.raises(ValueError) as excinfo:
-        m.proxy_add2(np.array([1., 2, 3]), 5.0)
-    assert msg(excinfo.value) == "array has incorrect number of dimensions: 1; expected 2"
+        m.proxy_add2(np.array([1.0, 2, 3]), 5.0)
+    assert (
+        msg(excinfo.value) == "array has incorrect number of dimensions: 1; expected 2"
+    )
 
-    expect_c = np.ndarray(shape=(3, 3, 3), buffer=np.array(range(3, 30)), dtype='int')
+    expect_c = np.ndarray(shape=(3, 3, 3), buffer=np.array(range(3, 30)), dtype="int")
     assert np.all(m.proxy_init3(3.0) == expect_c)
     expect_f = np.transpose(expect_c)
     assert np.all(m.proxy_init3F(3.0) == expect_f)
@@ -369,11 +413,11 @@ def test_array_unchecked_fixed_dims(msg):
 
 
 def test_array_unchecked_dyn_dims(msg):
-    z1 = np.array([[1, 2], [3, 4]], dtype='float64')
+    z1 = np.array([[1, 2], [3, 4]], dtype="float64")
     m.proxy_add2_dyn(z1, 10)
     assert np.all(z1 == [[11, 12], [13, 14]])
 
-    expect_c = np.ndarray(shape=(3, 3, 3), buffer=np.array(range(3, 30)), dtype='int')
+    expect_c = np.ndarray(shape=(3, 3, 3), buffer=np.array(range(3, 30)), dtype="int")
     assert np.all(m.proxy_init3_dyn(3.0) == expect_c)
 
     assert m.proxy_auxiliaries2_dyn(z1) == [11, 11, True, 2, 8, 2, 2, 4, 32]
@@ -383,15 +427,15 @@ def test_array_unchecked_dyn_dims(msg):
 def test_array_failure():
     with pytest.raises(ValueError) as excinfo:
         m.array_fail_test()
-    assert str(excinfo.value) == 'cannot create a pybind11::array from a nullptr'
+    assert str(excinfo.value) == "cannot create a pybind11::array from a nullptr"
 
     with pytest.raises(ValueError) as excinfo:
         m.array_t_fail_test()
-    assert str(excinfo.value) == 'cannot create a pybind11::array_t from a nullptr'
+    assert str(excinfo.value) == "cannot create a pybind11::array_t from a nullptr"
 
     with pytest.raises(ValueError) as excinfo:
         m.array_fail_test_negative_size()
-    assert str(excinfo.value) == 'negative dimensions are not allowed'
+    assert str(excinfo.value) == "negative dimensions are not allowed"
 
 
 def test_initializer_list():
@@ -402,35 +446,35 @@ def test_initializer_list():
 
 
 def test_array_resize(msg):
-    a = np.array([1, 2, 3, 4, 5, 6, 7, 8, 9], dtype='float64')
+    a = np.array([1, 2, 3, 4, 5, 6, 7, 8, 9], dtype="float64")
     m.array_reshape2(a)
-    assert(a.size == 9)
-    assert(np.all(a == [[1, 2, 3], [4, 5, 6], [7, 8, 9]]))
+    assert a.size == 9
+    assert np.all(a == [[1, 2, 3], [4, 5, 6], [7, 8, 9]])
 
     # total size change should succced with refcheck off
     m.array_resize3(a, 4, False)
-    assert(a.size == 64)
+    assert a.size == 64
     # ... and fail with refcheck on
     try:
         m.array_resize3(a, 3, True)
     except ValueError as e:
-        assert(str(e).startswith("cannot resize an array"))
+        assert str(e).startswith("cannot resize an array")
     # transposed array doesn't own data
     b = a.transpose()
     try:
         m.array_resize3(b, 3, False)
     except ValueError as e:
-        assert(str(e).startswith("cannot resize this array: it does not own its data"))
+        assert str(e).startswith("cannot resize this array: it does not own its data")
     # ... but reshape should be fine
     m.array_reshape2(b)
-    assert(b.shape == (8, 8))
+    assert b.shape == (8, 8)
 
 
 @pytest.mark.xfail("env.PYPY")
 def test_array_create_and_resize(msg):
     a = m.create_and_resize(2)
-    assert(a.size == 4)
-    assert(np.all(a == 42.))
+    assert a.size == 4
+    assert np.all(a == 42.0)
 
 
 def test_index_using_ellipsis():
@@ -439,16 +483,16 @@ def test_index_using_ellipsis():
 
 
 @pytest.mark.parametrize("forcecast", [False, True])
-@pytest.mark.parametrize("contiguity", [None, 'C', 'F'])
+@pytest.mark.parametrize("contiguity", [None, "C", "F"])
 @pytest.mark.parametrize("noconvert", [False, True])
 @pytest.mark.filterwarnings(
     "ignore:Casting complex values to real discards the imaginary part:numpy.ComplexWarning"
 )
 def test_argument_conversions(forcecast, contiguity, noconvert):
     function_name = "accept_double"
-    if contiguity == 'C':
+    if contiguity == "C":
         function_name += "_c_style"
-    elif contiguity == 'F':
+    elif contiguity == "F":
         function_name += "_f_style"
     if forcecast:
         function_name += "_forcecast"
@@ -456,37 +500,39 @@ def test_argument_conversions(forcecast, contiguity, noconvert):
         function_name += "_noconvert"
     function = getattr(m, function_name)
 
-    for dtype in [np.dtype('float32'), np.dtype('float64'), np.dtype('complex128')]:
-        for order in ['C', 'F']:
+    for dtype in [np.dtype("float32"), np.dtype("float64"), np.dtype("complex128")]:
+        for order in ["C", "F"]:
             for shape in [(2, 2), (1, 3, 1, 1), (1, 1, 1), (0,)]:
                 if not noconvert:
                     # If noconvert is not passed, only complex128 needs to be truncated and
                     # "cannot be safely obtained". So without `forcecast`, the argument shouldn't
                     # be accepted.
-                    should_raise = dtype.name == 'complex128' and not forcecast
+                    should_raise = dtype.name == "complex128" and not forcecast
                 else:
                     # If noconvert is passed, only float64 and the matching order is accepted.
                     # If at most one dimension has a size greater than 1, the array is also
                     # trivially contiguous.
                     trivially_contiguous = sum(1 for d in shape if d > 1) <= 1
-                    should_raise = (
-                        dtype.name != 'float64' or
-                        (contiguity is not None and
-                         contiguity != order and
-                         not trivially_contiguous)
+                    should_raise = dtype.name != "float64" or (
+                        contiguity is not None
+                        and contiguity != order
+                        and not trivially_contiguous
                     )
 
                 array = np.zeros(shape, dtype=dtype, order=order)
                 if not should_raise:
                     function(array)
                 else:
-                    with pytest.raises(TypeError, match="incompatible function arguments"):
+                    with pytest.raises(
+                        TypeError, match="incompatible function arguments"
+                    ):
                         function(array)
 
 
 @pytest.mark.xfail("env.PYPY")
 def test_dtype_refcount_leak():
     from sys import getrefcount
+
     dtype = np.dtype(np.float_)
     a = np.array([1], dtype=dtype)
     before = getrefcount(dtype)
diff --git a/tests/test_numpy_dtypes.py b/tests/test_numpy_dtypes.py
index b9f3bd26e..f56b776a4 100644
--- a/tests/test_numpy_dtypes.py
+++ b/tests/test_numpy_dtypes.py
@@ -10,57 +10,71 @@ from pybind11_tests import numpy_dtypes as m
 np = pytest.importorskip("numpy")
 
 
-@pytest.fixture(scope='module')
+@pytest.fixture(scope="module")
 def simple_dtype():
-    ld = np.dtype('longdouble')
-    return np.dtype({'names': ['bool_', 'uint_', 'float_', 'ldbl_'],
-                     'formats': ['?', 'u4', 'f4', 'f{}'.format(ld.itemsize)],
-                     'offsets': [0, 4, 8, (16 if ld.alignment > 4 else 12)]})
+    ld = np.dtype("longdouble")
+    return np.dtype(
+        {
+            "names": ["bool_", "uint_", "float_", "ldbl_"],
+            "formats": ["?", "u4", "f4", "f{}".format(ld.itemsize)],
+            "offsets": [0, 4, 8, (16 if ld.alignment > 4 else 12)],
+        }
+    )
 
 
-@pytest.fixture(scope='module')
+@pytest.fixture(scope="module")
 def packed_dtype():
-    return np.dtype([('bool_', '?'), ('uint_', 'u4'), ('float_', 'f4'), ('ldbl_', 'g')])
+    return np.dtype([("bool_", "?"), ("uint_", "u4"), ("float_", "f4"), ("ldbl_", "g")])
 
 
 def dt_fmt():
     from sys import byteorder
-    e = '<' if byteorder == 'little' else '>'
-    return ("{{'names':['bool_','uint_','float_','ldbl_'],"
-            " 'formats':['?','" + e + "u4','" + e + "f4','" + e + "f{}'],"
-            " 'offsets':[0,4,8,{}], 'itemsize':{}}}")
+
+    e = "<" if byteorder == "little" else ">"
+    return (
+        "{{'names':['bool_','uint_','float_','ldbl_'],"
+        " 'formats':['?','" + e + "u4','" + e + "f4','" + e + "f{}'],"
+        " 'offsets':[0,4,8,{}], 'itemsize':{}}}"
+    )
 
 
 def simple_dtype_fmt():
-    ld = np.dtype('longdouble')
+    ld = np.dtype("longdouble")
     simple_ld_off = 12 + 4 * (ld.alignment > 4)
     return dt_fmt().format(ld.itemsize, simple_ld_off, simple_ld_off + ld.itemsize)
 
 
 def packed_dtype_fmt():
     from sys import byteorder
+
     return "[('bool_', '?'), ('uint_', '{e}u4'), ('float_', '{e}f4'), ('ldbl_', '{e}f{}')]".format(
-        np.dtype('longdouble').itemsize, e='<' if byteorder == 'little' else '>')
+        np.dtype("longdouble").itemsize, e="<" if byteorder == "little" else ">"
+    )
 
 
 def partial_ld_offset():
-    return 12 + 4 * (np.dtype('uint64').alignment > 4) + 8 + 8 * (
-        np.dtype('longdouble').alignment > 8)
+    return (
+        12
+        + 4 * (np.dtype("uint64").alignment > 4)
+        + 8
+        + 8 * (np.dtype("longdouble").alignment > 8)
+    )
 
 
 def partial_dtype_fmt():
-    ld = np.dtype('longdouble')
+    ld = np.dtype("longdouble")
     partial_ld_off = partial_ld_offset()
     return dt_fmt().format(ld.itemsize, partial_ld_off, partial_ld_off + ld.itemsize)
 
 
 def partial_nested_fmt():
-    ld = np.dtype('longdouble')
+    ld = np.dtype("longdouble")
     partial_nested_off = 8 + 8 * (ld.alignment > 8)
     partial_ld_off = partial_ld_offset()
     partial_nested_size = partial_nested_off * 2 + partial_ld_off + ld.itemsize
     return "{{'names':['a'], 'formats':[{}], 'offsets':[{}], 'itemsize':{}}}".format(
-        partial_dtype_fmt(), partial_nested_off, partial_nested_size)
+        partial_dtype_fmt(), partial_nested_off, partial_nested_size
+    )
 
 
 def assert_equal(actual, expected_data, expected_dtype):
@@ -70,15 +84,19 @@ def assert_equal(actual, expected_data, expected_dtype):
 def test_format_descriptors():
     with pytest.raises(RuntimeError) as excinfo:
         m.get_format_unbound()
-    assert re.match('^NumPy type info missing for .*UnboundStruct.*$', str(excinfo.value))
+    assert re.match(
+        "^NumPy type info missing for .*UnboundStruct.*$", str(excinfo.value)
+    )
 
-    ld = np.dtype('longdouble')
-    ldbl_fmt = ('4x' if ld.alignment > 4 else '') + ld.char
+    ld = np.dtype("longdouble")
+    ldbl_fmt = ("4x" if ld.alignment > 4 else "") + ld.char
     ss_fmt = "^T{?:bool_:3xI:uint_:f:float_:" + ldbl_fmt + ":ldbl_:}"
-    dbl = np.dtype('double')
-    partial_fmt = ("^T{?:bool_:3xI:uint_:f:float_:" +
-                   str(4 * (dbl.alignment > 4) + dbl.itemsize + 8 * (ld.alignment > 8)) +
-                   "xg:ldbl_:}")
+    dbl = np.dtype("double")
+    partial_fmt = (
+        "^T{?:bool_:3xI:uint_:f:float_:"
+        + str(4 * (dbl.alignment > 4) + dbl.itemsize + 8 * (ld.alignment > 8))
+        + "xg:ldbl_:}"
+    )
     nested_extra = str(max(8, ld.alignment))
     assert m.print_format_descriptors() == [
         ss_fmt,
@@ -88,14 +106,15 @@ def test_format_descriptors():
         "^T{" + nested_extra + "x" + partial_fmt + ":a:" + nested_extra + "x}",
         "^T{3s:a:3s:b:}",
         "^T{(3)4s:a:(2)i:b:(3)B:c:1x(4, 2)f:d:}",
-        '^T{q:e1:B:e2:}',
-        '^T{Zf:cflt:Zd:cdbl:}'
+        "^T{q:e1:B:e2:}",
+        "^T{Zf:cflt:Zd:cdbl:}",
     ]
 
 
 def test_dtype(simple_dtype):
     from sys import byteorder
-    e = '<' if byteorder == 'little' else '>'
+
+    e = "<" if byteorder == "little" else ">"
 
     assert m.print_dtypes() == [
         simple_dtype_fmt(),
@@ -104,30 +123,60 @@ def test_dtype(simple_dtype):
         partial_dtype_fmt(),
         partial_nested_fmt(),
         "[('a', 'S3'), ('b', 'S3')]",
-        ("{{'names':['a','b','c','d'], " +
-         "'formats':[('S4', (3,)),('" + e + "i4', (2,)),('u1', (3,)),('" + e + "f4', (4, 2))], " +
-         "'offsets':[0,12,20,24], 'itemsize':56}}").format(e=e),
+        (
+            "{{'names':['a','b','c','d'], "
+            + "'formats':[('S4', (3,)),('"
+            + e
+            + "i4', (2,)),('u1', (3,)),('"
+            + e
+            + "f4', (4, 2))], "
+            + "'offsets':[0,12,20,24], 'itemsize':56}}"
+        ).format(e=e),
         "[('e1', '" + e + "i8'), ('e2', 'u1')]",
         "[('x', 'i1'), ('y', '" + e + "u8')]",
-        "[('cflt', '" + e + "c8'), ('cdbl', '" + e + "c16')]"
+        "[('cflt', '" + e + "c8'), ('cdbl', '" + e + "c16')]",
     ]
 
-    d1 = np.dtype({'names': ['a', 'b'], 'formats': ['int32', 'float64'],
-                   'offsets': [1, 10], 'itemsize': 20})
-    d2 = np.dtype([('a', 'i4'), ('b', 'f4')])
-    assert m.test_dtype_ctors() == [np.dtype('int32'), np.dtype('float64'),
-                                    np.dtype('bool'), d1, d1, np.dtype('uint32'), d2]
+    d1 = np.dtype(
+        {
+            "names": ["a", "b"],
+            "formats": ["int32", "float64"],
+            "offsets": [1, 10],
+            "itemsize": 20,
+        }
+    )
+    d2 = np.dtype([("a", "i4"), ("b", "f4")])
+    assert m.test_dtype_ctors() == [
+        np.dtype("int32"),
+        np.dtype("float64"),
+        np.dtype("bool"),
+        d1,
+        d1,
+        np.dtype("uint32"),
+        d2,
+    ]
 
-    assert m.test_dtype_methods() == [np.dtype('int32'), simple_dtype, False, True,
-                                      np.dtype('int32').itemsize, simple_dtype.itemsize]
+    assert m.test_dtype_methods() == [
+        np.dtype("int32"),
+        simple_dtype,
+        False,
+        True,
+        np.dtype("int32").itemsize,
+        simple_dtype.itemsize,
+    ]
 
-    assert m.trailing_padding_dtype() == m.buffer_to_dtype(np.zeros(1, m.trailing_padding_dtype()))
+    assert m.trailing_padding_dtype() == m.buffer_to_dtype(
+        np.zeros(1, m.trailing_padding_dtype())
+    )
 
 
 def test_recarray(simple_dtype, packed_dtype):
     elements = [(False, 0, 0.0, -0.0), (True, 1, 1.5, -2.5), (False, 2, 3.0, -5.0)]
 
-    for func, dtype in [(m.create_rec_simple, simple_dtype), (m.create_rec_packed, packed_dtype)]:
+    for func, dtype in [
+        (m.create_rec_simple, simple_dtype),
+        (m.create_rec_packed, packed_dtype),
+    ]:
         arr = func(0)
         assert arr.dtype == dtype
         assert_equal(arr, [], simple_dtype)
@@ -146,16 +195,16 @@ def test_recarray(simple_dtype, packed_dtype):
             assert m.print_rec_simple(arr) == [
                 "s:0,0,0,-0",
                 "s:1,1,1.5,-2.5",
-                "s:0,2,3,-5"
+                "s:0,2,3,-5",
             ]
         else:
             assert m.print_rec_packed(arr) == [
                 "p:0,0,0,-0",
                 "p:1,1,1.5,-2.5",
-                "p:0,2,3,-5"
+                "p:0,2,3,-5",
             ]
 
-    nested_dtype = np.dtype([('a', simple_dtype), ('b', packed_dtype)])
+    nested_dtype = np.dtype([("a", simple_dtype), ("b", packed_dtype)])
 
     arr = m.create_rec_nested(0)
     assert arr.dtype == nested_dtype
@@ -163,33 +212,39 @@ def test_recarray(simple_dtype, packed_dtype):
 
     arr = m.create_rec_nested(3)
     assert arr.dtype == nested_dtype
-    assert_equal(arr, [((False, 0, 0.0, -0.0), (True, 1, 1.5, -2.5)),
-                       ((True, 1, 1.5, -2.5), (False, 2, 3.0, -5.0)),
-                       ((False, 2, 3.0, -5.0), (True, 3, 4.5, -7.5))], nested_dtype)
+    assert_equal(
+        arr,
+        [
+            ((False, 0, 0.0, -0.0), (True, 1, 1.5, -2.5)),
+            ((True, 1, 1.5, -2.5), (False, 2, 3.0, -5.0)),
+            ((False, 2, 3.0, -5.0), (True, 3, 4.5, -7.5)),
+        ],
+        nested_dtype,
+    )
     assert m.print_rec_nested(arr) == [
         "n:a=s:0,0,0,-0;b=p:1,1,1.5,-2.5",
         "n:a=s:1,1,1.5,-2.5;b=p:0,2,3,-5",
-        "n:a=s:0,2,3,-5;b=p:1,3,4.5,-7.5"
+        "n:a=s:0,2,3,-5;b=p:1,3,4.5,-7.5",
     ]
 
     arr = m.create_rec_partial(3)
     assert str(arr.dtype) == partial_dtype_fmt()
     partial_dtype = arr.dtype
-    assert '' not in arr.dtype.fields
+    assert "" not in arr.dtype.fields
     assert partial_dtype.itemsize > simple_dtype.itemsize
     assert_equal(arr, elements, simple_dtype)
     assert_equal(arr, elements, packed_dtype)
 
     arr = m.create_rec_partial_nested(3)
     assert str(arr.dtype) == partial_nested_fmt()
-    assert '' not in arr.dtype.fields
-    assert '' not in arr.dtype.fields['a'][0].fields
+    assert "" not in arr.dtype.fields
+    assert "" not in arr.dtype.fields["a"][0].fields
     assert arr.dtype.itemsize > partial_dtype.itemsize
-    np.testing.assert_equal(arr['a'], m.create_rec_partial(3))
+    np.testing.assert_equal(arr["a"], m.create_rec_partial(3))
 
 
 def test_array_constructors():
-    data = np.arange(1, 7, dtype='int32')
+    data = np.arange(1, 7, dtype="int32")
     for i in range(8):
         np.testing.assert_array_equal(m.test_array_ctors(10 + i), data.reshape((3, 2)))
         np.testing.assert_array_equal(m.test_array_ctors(20 + i), data.reshape((3, 2)))
@@ -205,82 +260,92 @@ def test_string_array():
         "a='',b=''",
         "a='a',b='a'",
         "a='ab',b='ab'",
-        "a='abc',b='abc'"
+        "a='abc',b='abc'",
     ]
     dtype = arr.dtype
-    assert arr['a'].tolist() == [b'', b'a', b'ab', b'abc']
-    assert arr['b'].tolist() == [b'', b'a', b'ab', b'abc']
+    assert arr["a"].tolist() == [b"", b"a", b"ab", b"abc"]
+    assert arr["b"].tolist() == [b"", b"a", b"ab", b"abc"]
     arr = m.create_string_array(False)
     assert dtype == arr.dtype
 
 
 def test_array_array():
     from sys import byteorder
-    e = '<' if byteorder == 'little' else '>'
+
+    e = "<" if byteorder == "little" else ">"
 
     arr = m.create_array_array(3)
     assert str(arr.dtype) == (
-        "{{'names':['a','b','c','d'], " +
-        "'formats':[('S4', (3,)),('" + e + "i4', (2,)),('u1', (3,)),('{e}f4', (4, 2))], " +
-        "'offsets':[0,12,20,24], 'itemsize':56}}").format(e=e)
+        "{{'names':['a','b','c','d'], "
+        + "'formats':[('S4', (3,)),('"
+        + e
+        + "i4', (2,)),('u1', (3,)),('{e}f4', (4, 2))], "
+        + "'offsets':[0,12,20,24], 'itemsize':56}}"
+    ).format(e=e)
     assert m.print_array_array(arr) == [
-        "a={{A,B,C,D},{K,L,M,N},{U,V,W,X}},b={0,1}," +
-        "c={0,1,2},d={{0,1},{10,11},{20,21},{30,31}}",
-        "a={{W,X,Y,Z},{G,H,I,J},{Q,R,S,T}},b={1000,1001}," +
-        "c={10,11,12},d={{100,101},{110,111},{120,121},{130,131}}",
-        "a={{S,T,U,V},{C,D,E,F},{M,N,O,P}},b={2000,2001}," +
-        "c={20,21,22},d={{200,201},{210,211},{220,221},{230,231}}",
+        "a={{A,B,C,D},{K,L,M,N},{U,V,W,X}},b={0,1},"
+        + "c={0,1,2},d={{0,1},{10,11},{20,21},{30,31}}",
+        "a={{W,X,Y,Z},{G,H,I,J},{Q,R,S,T}},b={1000,1001},"
+        + "c={10,11,12},d={{100,101},{110,111},{120,121},{130,131}}",
+        "a={{S,T,U,V},{C,D,E,F},{M,N,O,P}},b={2000,2001},"
+        + "c={20,21,22},d={{200,201},{210,211},{220,221},{230,231}}",
     ]
-    assert arr['a'].tolist() == [[b'ABCD', b'KLMN', b'UVWX'],
-                                 [b'WXYZ', b'GHIJ', b'QRST'],
-                                 [b'STUV', b'CDEF', b'MNOP']]
-    assert arr['b'].tolist() == [[0, 1], [1000, 1001], [2000, 2001]]
+    assert arr["a"].tolist() == [
+        [b"ABCD", b"KLMN", b"UVWX"],
+        [b"WXYZ", b"GHIJ", b"QRST"],
+        [b"STUV", b"CDEF", b"MNOP"],
+    ]
+    assert arr["b"].tolist() == [[0, 1], [1000, 1001], [2000, 2001]]
     assert m.create_array_array(0).dtype == arr.dtype
 
 
 def test_enum_array():
     from sys import byteorder
-    e = '<' if byteorder == 'little' else '>'
+
+    e = "<" if byteorder == "little" else ">"
 
     arr = m.create_enum_array(3)
     dtype = arr.dtype
-    assert dtype == np.dtype([('e1', e + 'i8'), ('e2', 'u1')])
-    assert m.print_enum_array(arr) == [
-        "e1=A,e2=X",
-        "e1=B,e2=Y",
-        "e1=A,e2=X"
-    ]
-    assert arr['e1'].tolist() == [-1, 1, -1]
-    assert arr['e2'].tolist() == [1, 2, 1]
+    assert dtype == np.dtype([("e1", e + "i8"), ("e2", "u1")])
+    assert m.print_enum_array(arr) == ["e1=A,e2=X", "e1=B,e2=Y", "e1=A,e2=X"]
+    assert arr["e1"].tolist() == [-1, 1, -1]
+    assert arr["e2"].tolist() == [1, 2, 1]
     assert m.create_enum_array(0).dtype == dtype
 
 
 def test_complex_array():
     from sys import byteorder
-    e = '<' if byteorder == 'little' else '>'
+
+    e = "<" if byteorder == "little" else ">"
 
     arr = m.create_complex_array(3)
     dtype = arr.dtype
-    assert dtype == np.dtype([('cflt', e + 'c8'), ('cdbl', e + 'c16')])
+    assert dtype == np.dtype([("cflt", e + "c8"), ("cdbl", e + "c16")])
     assert m.print_complex_array(arr) == [
         "c:(0,0.25),(0.5,0.75)",
         "c:(1,1.25),(1.5,1.75)",
-        "c:(2,2.25),(2.5,2.75)"
+        "c:(2,2.25),(2.5,2.75)",
     ]
-    assert arr['cflt'].tolist() == [0.0 + 0.25j, 1.0 + 1.25j, 2.0 + 2.25j]
-    assert arr['cdbl'].tolist() == [0.5 + 0.75j, 1.5 + 1.75j, 2.5 + 2.75j]
+    assert arr["cflt"].tolist() == [0.0 + 0.25j, 1.0 + 1.25j, 2.0 + 2.25j]
+    assert arr["cdbl"].tolist() == [0.5 + 0.75j, 1.5 + 1.75j, 2.5 + 2.75j]
     assert m.create_complex_array(0).dtype == dtype
 
 
 def test_signature(doc):
-    assert doc(m.create_rec_nested) == \
-        "create_rec_nested(arg0: int) -> numpy.ndarray[NestedStruct]"
+    assert (
+        doc(m.create_rec_nested)
+        == "create_rec_nested(arg0: int) -> numpy.ndarray[NestedStruct]"
+    )
 
 
 def test_scalar_conversion():
     n = 3
-    arrays = [m.create_rec_simple(n), m.create_rec_packed(n),
-              m.create_rec_nested(n), m.create_enum_array(n)]
+    arrays = [
+        m.create_rec_simple(n),
+        m.create_rec_packed(n),
+        m.create_rec_nested(n),
+        m.create_enum_array(n),
+    ]
     funcs = [m.f_simple, m.f_packed, m.f_nested]
 
     for i, func in enumerate(funcs):
@@ -290,7 +355,7 @@ def test_scalar_conversion():
             else:
                 with pytest.raises(TypeError) as excinfo:
                     func(arr[0])
-                assert 'incompatible function arguments' in str(excinfo.value)
+                assert "incompatible function arguments" in str(excinfo.value)
 
 
 def test_vectorize():
@@ -304,14 +369,14 @@ def test_vectorize():
 
 def test_cls_and_dtype_conversion(simple_dtype):
     s = m.SimpleStruct()
-    assert s.astuple() == (False, 0, 0., 0.)
+    assert s.astuple() == (False, 0, 0.0, 0.0)
     assert m.SimpleStruct.fromtuple(s.astuple()).astuple() == s.astuple()
 
     s.uint_ = 2
     assert m.f_simple(s) == 20
 
     # Try as recarray of shape==(1,).
-    s_recarray = np.array([(False, 2, 0., 0.)], dtype=simple_dtype)
+    s_recarray = np.array([(False, 2, 0.0, 0.0)], dtype=simple_dtype)
     # Show that this will work for vectorized case.
     np.testing.assert_array_equal(m.f_simple_vectorized(s_recarray), [20])
 
@@ -327,17 +392,16 @@ def test_cls_and_dtype_conversion(simple_dtype):
     assert s_recarray_scalar.dtype == simple_dtype
     with pytest.raises(TypeError) as excinfo:
         m.f_simple(s_recarray_scalar)
-    assert 'incompatible function arguments' in str(excinfo.value)
+    assert "incompatible function arguments" in str(excinfo.value)
     # Explicitly convert to m.SimpleStruct.
-    assert m.f_simple(
-        m.SimpleStruct.fromtuple(s_recarray_scalar.item())) == 20
+    assert m.f_simple(m.SimpleStruct.fromtuple(s_recarray_scalar.item())) == 20
 
     # Show that an array of dtype=object does *not* convert.
     s_array_object = np.array([s])
     assert s_array_object.dtype == object
     with pytest.raises(TypeError) as excinfo:
         m.f_simple_vectorized(s_array_object)
-    assert 'incompatible function arguments' in str(excinfo.value)
+    assert "incompatible function arguments" in str(excinfo.value)
     # Explicitly convert to `np.array(..., dtype=simple_dtype)`
     s_array = np.array([s.astuple()], dtype=simple_dtype)
     np.testing.assert_array_equal(m.f_simple_vectorized(s_array), [20])
@@ -346,12 +410,13 @@ def test_cls_and_dtype_conversion(simple_dtype):
 def test_register_dtype():
     with pytest.raises(RuntimeError) as excinfo:
         m.register_dtype()
-    assert 'dtype is already registered' in str(excinfo.value)
+    assert "dtype is already registered" in str(excinfo.value)
 
 
 @pytest.mark.xfail("env.PYPY")
 def test_str_leak():
     from sys import getrefcount
+
     fmt = "f4"
     pytest.gc_collect()
     start = getrefcount(fmt)
diff --git a/tests/test_numpy_vectorize.py b/tests/test_numpy_vectorize.py
index 992ff8ecc..4e6b2d198 100644
--- a/tests/test_numpy_vectorize.py
+++ b/tests/test_numpy_vectorize.py
@@ -17,28 +17,40 @@ def test_vectorize(capture):
         assert capture == "my_func(x:int=1, y:float=2, z:float=3)"
         with capture:
             assert np.allclose(f(np.array([1, 3]), np.array([2, 4]), 3), [6, 36])
-        assert capture == """
+        assert (
+            capture
+            == """
             my_func(x:int=1, y:float=2, z:float=3)
             my_func(x:int=3, y:float=4, z:float=3)
         """
+        )
         with capture:
-            a = np.array([[1, 2], [3, 4]], order='F')
-            b = np.array([[10, 20], [30, 40]], order='F')
+            a = np.array([[1, 2], [3, 4]], order="F")
+            b = np.array([[10, 20], [30, 40]], order="F")
             c = 3
             result = f(a, b, c)
             assert np.allclose(result, a * b * c)
             assert result.flags.f_contiguous
         # All inputs are F order and full or singletons, so we the result is in col-major order:
-        assert capture == """
+        assert (
+            capture
+            == """
             my_func(x:int=1, y:float=10, z:float=3)
             my_func(x:int=3, y:float=30, z:float=3)
             my_func(x:int=2, y:float=20, z:float=3)
             my_func(x:int=4, y:float=40, z:float=3)
         """
+        )
         with capture:
-            a, b, c = np.array([[1, 3, 5], [7, 9, 11]]), np.array([[2, 4, 6], [8, 10, 12]]), 3
+            a, b, c = (
+                np.array([[1, 3, 5], [7, 9, 11]]),
+                np.array([[2, 4, 6], [8, 10, 12]]),
+                3,
+            )
             assert np.allclose(f(a, b, c), a * b * c)
-        assert capture == """
+        assert (
+            capture
+            == """
             my_func(x:int=1, y:float=2, z:float=3)
             my_func(x:int=3, y:float=4, z:float=3)
             my_func(x:int=5, y:float=6, z:float=3)
@@ -46,10 +58,13 @@ def test_vectorize(capture):
             my_func(x:int=9, y:float=10, z:float=3)
             my_func(x:int=11, y:float=12, z:float=3)
         """
+        )
         with capture:
             a, b, c = np.array([[1, 2, 3], [4, 5, 6]]), np.array([2, 3, 4]), 2
             assert np.allclose(f(a, b, c), a * b * c)
-        assert capture == """
+        assert (
+            capture
+            == """
             my_func(x:int=1, y:float=2, z:float=2)
             my_func(x:int=2, y:float=3, z:float=2)
             my_func(x:int=3, y:float=4, z:float=2)
@@ -57,10 +72,13 @@ def test_vectorize(capture):
             my_func(x:int=5, y:float=3, z:float=2)
             my_func(x:int=6, y:float=4, z:float=2)
         """
+        )
         with capture:
             a, b, c = np.array([[1, 2, 3], [4, 5, 6]]), np.array([[2], [3]]), 2
             assert np.allclose(f(a, b, c), a * b * c)
-        assert capture == """
+        assert (
+            capture
+            == """
             my_func(x:int=1, y:float=2, z:float=2)
             my_func(x:int=2, y:float=2, z:float=2)
             my_func(x:int=3, y:float=2, z:float=2)
@@ -68,10 +86,17 @@ def test_vectorize(capture):
             my_func(x:int=5, y:float=3, z:float=2)
             my_func(x:int=6, y:float=3, z:float=2)
         """
+        )
         with capture:
-            a, b, c = np.array([[1, 2, 3], [4, 5, 6]], order='F'), np.array([[2], [3]]), 2
+            a, b, c = (
+                np.array([[1, 2, 3], [4, 5, 6]], order="F"),
+                np.array([[2], [3]]),
+                2,
+            )
             assert np.allclose(f(a, b, c), a * b * c)
-        assert capture == """
+        assert (
+            capture
+            == """
             my_func(x:int=1, y:float=2, z:float=2)
             my_func(x:int=2, y:float=2, z:float=2)
             my_func(x:int=3, y:float=2, z:float=2)
@@ -79,36 +104,53 @@ def test_vectorize(capture):
             my_func(x:int=5, y:float=3, z:float=2)
             my_func(x:int=6, y:float=3, z:float=2)
         """
+        )
         with capture:
             a, b, c = np.array([[1, 2, 3], [4, 5, 6]])[::, ::2], np.array([[2], [3]]), 2
             assert np.allclose(f(a, b, c), a * b * c)
-        assert capture == """
+        assert (
+            capture
+            == """
             my_func(x:int=1, y:float=2, z:float=2)
             my_func(x:int=3, y:float=2, z:float=2)
             my_func(x:int=4, y:float=3, z:float=2)
             my_func(x:int=6, y:float=3, z:float=2)
         """
+        )
         with capture:
-            a, b, c = np.array([[1, 2, 3], [4, 5, 6]], order='F')[::, ::2], np.array([[2], [3]]), 2
+            a, b, c = (
+                np.array([[1, 2, 3], [4, 5, 6]], order="F")[::, ::2],
+                np.array([[2], [3]]),
+                2,
+            )
             assert np.allclose(f(a, b, c), a * b * c)
-        assert capture == """
+        assert (
+            capture
+            == """
             my_func(x:int=1, y:float=2, z:float=2)
             my_func(x:int=3, y:float=2, z:float=2)
             my_func(x:int=4, y:float=3, z:float=2)
             my_func(x:int=6, y:float=3, z:float=2)
         """
+        )
 
 
 def test_type_selection():
     assert m.selective_func(np.array([1], dtype=np.int32)) == "Int branch taken."
     assert m.selective_func(np.array([1.0], dtype=np.float32)) == "Float branch taken."
-    assert m.selective_func(np.array([1.0j], dtype=np.complex64)) == "Complex float branch taken."
+    assert (
+        m.selective_func(np.array([1.0j], dtype=np.complex64))
+        == "Complex float branch taken."
+    )
 
 
 def test_docs(doc):
-    assert doc(m.vectorized_func) == """
+    assert (
+        doc(m.vectorized_func)
+        == """
         vectorized_func(arg0: numpy.ndarray[numpy.int32], arg1: numpy.ndarray[numpy.float32], arg2: numpy.ndarray[numpy.float64]) -> object
     """  # noqa: E501 line too long
+    )
 
 
 def test_trivial_broadcasting():
@@ -116,16 +158,24 @@ def test_trivial_broadcasting():
 
     assert vectorized_is_trivial(1, 2, 3) == trivial.c_trivial
     assert vectorized_is_trivial(np.array(1), np.array(2), 3) == trivial.c_trivial
-    assert vectorized_is_trivial(np.array([1, 3]), np.array([2, 4]), 3) == trivial.c_trivial
+    assert (
+        vectorized_is_trivial(np.array([1, 3]), np.array([2, 4]), 3)
+        == trivial.c_trivial
+    )
     assert trivial.c_trivial == vectorized_is_trivial(
-        np.array([[1, 3, 5], [7, 9, 11]]), np.array([[2, 4, 6], [8, 10, 12]]), 3)
-    assert vectorized_is_trivial(
-        np.array([[1, 2, 3], [4, 5, 6]]), np.array([2, 3, 4]), 2) == trivial.non_trivial
-    assert vectorized_is_trivial(
-        np.array([[1, 2, 3], [4, 5, 6]]), np.array([[2], [3]]), 2) == trivial.non_trivial
-    z1 = np.array([[1, 2, 3, 4], [5, 6, 7, 8]], dtype='int32')
-    z2 = np.array(z1, dtype='float32')
-    z3 = np.array(z1, dtype='float64')
+        np.array([[1, 3, 5], [7, 9, 11]]), np.array([[2, 4, 6], [8, 10, 12]]), 3
+    )
+    assert (
+        vectorized_is_trivial(np.array([[1, 2, 3], [4, 5, 6]]), np.array([2, 3, 4]), 2)
+        == trivial.non_trivial
+    )
+    assert (
+        vectorized_is_trivial(np.array([[1, 2, 3], [4, 5, 6]]), np.array([[2], [3]]), 2)
+        == trivial.non_trivial
+    )
+    z1 = np.array([[1, 2, 3, 4], [5, 6, 7, 8]], dtype="int32")
+    z2 = np.array(z1, dtype="float32")
+    z3 = np.array(z1, dtype="float64")
     assert vectorized_is_trivial(z1, z2, z3) == trivial.c_trivial
     assert vectorized_is_trivial(1, z2, z3) == trivial.c_trivial
     assert vectorized_is_trivial(z1, 1, z3) == trivial.c_trivial
@@ -135,7 +185,7 @@ def test_trivial_broadcasting():
     assert vectorized_is_trivial(1, 1, z3[::2, ::2]) == trivial.non_trivial
     assert vectorized_is_trivial(z1, 1, z3[1::4, 1::4]) == trivial.c_trivial
 
-    y1 = np.array(z1, order='F')
+    y1 = np.array(z1, order="F")
     y2 = np.array(y1)
     y3 = np.array(y1)
     assert vectorized_is_trivial(y1, y2, y3) == trivial.f_trivial
@@ -156,30 +206,41 @@ def test_trivial_broadcasting():
 
 def test_passthrough_arguments(doc):
     assert doc(m.vec_passthrough) == (
-        "vec_passthrough(" + ", ".join([
-            "arg0: float",
-            "arg1: numpy.ndarray[numpy.float64]",
-            "arg2: numpy.ndarray[numpy.float64]",
-            "arg3: numpy.ndarray[numpy.int32]",
-            "arg4: int",
-            "arg5: m.numpy_vectorize.NonPODClass",
-            "arg6: numpy.ndarray[numpy.float64]"]) + ") -> object")
+        "vec_passthrough("
+        + ", ".join(
+            [
+                "arg0: float",
+                "arg1: numpy.ndarray[numpy.float64]",
+                "arg2: numpy.ndarray[numpy.float64]",
+                "arg3: numpy.ndarray[numpy.int32]",
+                "arg4: int",
+                "arg5: m.numpy_vectorize.NonPODClass",
+                "arg6: numpy.ndarray[numpy.float64]",
+            ]
+        )
+        + ") -> object"
+    )
 
-    b = np.array([[10, 20, 30]], dtype='float64')
+    b = np.array([[10, 20, 30]], dtype="float64")
     c = np.array([100, 200])  # NOT a vectorized argument
-    d = np.array([[1000], [2000], [3000]], dtype='int')
-    g = np.array([[1000000, 2000000, 3000000]], dtype='int')  # requires casting
+    d = np.array([[1000], [2000], [3000]], dtype="int")
+    g = np.array([[1000000, 2000000, 3000000]], dtype="int")  # requires casting
     assert np.all(
-        m.vec_passthrough(1, b, c, d, 10000, m.NonPODClass(100000), g) ==
-        np.array([[1111111, 2111121, 3111131],
-                  [1112111, 2112121, 3112131],
-                  [1113111, 2113121, 3113131]]))
+        m.vec_passthrough(1, b, c, d, 10000, m.NonPODClass(100000), g)
+        == np.array(
+            [
+                [1111111, 2111121, 3111131],
+                [1112111, 2112121, 3112131],
+                [1113111, 2113121, 3113131],
+            ]
+        )
+    )
 
 
 def test_method_vectorization():
     o = m.VectorizeTestClass(3)
-    x = np.array([1, 2], dtype='int')
-    y = np.array([[10], [20]], dtype='float32')
+    x = np.array([1, 2], dtype="int")
+    y = np.array([[10], [20]], dtype="float32")
     assert np.all(o.method(x, y) == [[14, 15], [24, 25]])
 
 
@@ -188,7 +249,7 @@ def test_array_collapse():
     assert not isinstance(m.vectorized_func(np.array(1), 2, 3), np.ndarray)
     z = m.vectorized_func([1], 2, 3)
     assert isinstance(z, np.ndarray)
-    assert z.shape == (1, )
+    assert z.shape == (1,)
     z = m.vectorized_func(1, [[[2]]], 3)
     assert isinstance(z, np.ndarray)
     assert z.shape == (1, 1, 1)
diff --git a/tests/test_opaque_types.py b/tests/test_opaque_types.py
index ac6a8560e..773794634 100644
--- a/tests/test_opaque_types.py
+++ b/tests/test_opaque_types.py
@@ -32,12 +32,15 @@ def test_pointers(msg):
 
     with pytest.raises(TypeError) as excinfo:
         m.get_void_ptr_value([1, 2, 3])  # This should not work
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         get_void_ptr_value(): incompatible function arguments. The following argument types are supported:
             1. (arg0: capsule) -> int
 
         Invoked with: [1, 2, 3]
     """  # noqa: E501 line too long
+    )
 
     assert m.return_null_str() is None
     assert m.get_null_str_value(m.return_null_str()) is not None
diff --git a/tests/test_operator_overloading.py b/tests/test_operator_overloading.py
index 39e3aee27..5dbfb32c8 100644
--- a/tests/test_operator_overloading.py
+++ b/tests/test_operator_overloading.py
@@ -56,23 +56,23 @@ def test_operator_overloading():
     del v3
     assert cstats.alive() == 0
     assert cstats.values() == [
-        '[1.000000, 2.000000]',
-        '[3.000000, -1.000000]',
-        '[1.000000, 2.000000]',
-        '[-3.000000, 1.000000]',
-        '[4.000000, 1.000000]',
-        '[-2.000000, 3.000000]',
-        '[-7.000000, -6.000000]',
-        '[9.000000, 10.000000]',
-        '[8.000000, 16.000000]',
-        '[0.125000, 0.250000]',
-        '[7.000000, 6.000000]',
-        '[9.000000, 10.000000]',
-        '[8.000000, 16.000000]',
-        '[8.000000, 4.000000]',
-        '[3.000000, -2.000000]',
-        '[3.000000, -0.500000]',
-        '[6.000000, -2.000000]',
+        "[1.000000, 2.000000]",
+        "[3.000000, -1.000000]",
+        "[1.000000, 2.000000]",
+        "[-3.000000, 1.000000]",
+        "[4.000000, 1.000000]",
+        "[-2.000000, 3.000000]",
+        "[-7.000000, -6.000000]",
+        "[9.000000, 10.000000]",
+        "[8.000000, 16.000000]",
+        "[0.125000, 0.250000]",
+        "[7.000000, 6.000000]",
+        "[9.000000, 10.000000]",
+        "[8.000000, 16.000000]",
+        "[8.000000, 4.000000]",
+        "[3.000000, -2.000000]",
+        "[3.000000, -0.500000]",
+        "[6.000000, -2.000000]",
     ]
     assert cstats.default_constructions == 0
     assert cstats.copy_constructions == 0
diff --git a/tests/test_pickling.py b/tests/test_pickling.py
index 9aee70505..6b27a73a5 100644
--- a/tests/test_pickling.py
+++ b/tests/test_pickling.py
@@ -42,5 +42,6 @@ def test_roundtrip_with_dict(cls_name):
 
 def test_enum_pickle():
     from pybind11_tests import enums as e
+
     data = pickle.dumps(e.EOne, 2)
     assert e.EOne == pickle.loads(data)
diff --git a/tests/test_pytypes.py b/tests/test_pytypes.py
index 403c4da4b..9e5c302e5 100644
--- a/tests/test_pytypes.py
+++ b/tests/test_pytypes.py
@@ -28,13 +28,16 @@ def test_list(capture, doc):
 
         lst.append("value2")
         m.print_list(lst)
-    assert capture.unordered == """
+    assert (
+        capture.unordered
+        == """
         Entry at position 0: value
         list item 0: inserted-0
         list item 1: overwritten
         list item 2: inserted-2
         list item 3: value2
     """
+    )
 
     assert doc(m.get_list) == "get_list() -> list"
     assert doc(m.print_list) == "print_list(arg0: list) -> None"
@@ -52,12 +55,15 @@ def test_set(capture, doc):
     with capture:
         s.add("key4")
         m.print_set(s)
-    assert capture.unordered == """
+    assert (
+        capture.unordered
+        == """
         key: key1
         key: key2
         key: key3
         key: key4
     """
+    )
 
     assert not m.set_contains(set([]), 42)
     assert m.set_contains({42}, 42)
@@ -74,10 +80,13 @@ def test_dict(capture, doc):
     with capture:
         d["key2"] = "value2"
         m.print_dict(d)
-    assert capture.unordered == """
+    assert (
+        capture.unordered
+        == """
         key: key, value=value
         key: key2, value=value2
     """
+    )
 
     assert not m.dict_contains({}, 42)
     assert m.dict_contains({42: None}, 42)
@@ -137,28 +146,37 @@ def test_capsule(capture):
         a = m.return_capsule_with_destructor()
         del a
         pytest.gc_collect()
-    assert capture.unordered == """
+    assert (
+        capture.unordered
+        == """
         creating capsule
         destructing capsule
     """
+    )
 
     with capture:
         a = m.return_capsule_with_destructor_2()
         del a
         pytest.gc_collect()
-    assert capture.unordered == """
+    assert (
+        capture.unordered
+        == """
         creating capsule
         destructing capsule: 1234
     """
+    )
 
     with capture:
         a = m.return_capsule_with_name_and_destructor()
         del a
         pytest.gc_collect()
-    assert capture.unordered == """
+    assert (
+        capture.unordered
+        == """
         created capsule (1234, 'pointer type description')
         destructing capsule (1234, 'pointer type description')
     """
+    )
 
 
 def test_accessors():
@@ -212,7 +230,7 @@ def test_constructors():
     assert m.default_constructors() == expected
 
     data = {
-        bytes: b'41',  # Currently no supported or working conversions.
+        bytes: b"41",  # Currently no supported or working conversions.
         str: 42,
         bool: "Not empty",
         int: "42",
@@ -221,14 +239,14 @@ def test_constructors():
         list: range(3),
         dict: [("two", 2), ("one", 1), ("three", 3)],
         set: [4, 4, 5, 6, 6, 6],
-        memoryview: b'abc'
+        memoryview: b"abc",
     }
     inputs = {k.__name__: v for k, v in data.items()}
     expected = {k.__name__: k(v) for k, v in data.items()}
     if env.PY2:  # Similar to the above. See comments above.
-        inputs["bytes"] = b'41'
+        inputs["bytes"] = b"41"
         inputs["str"] = 42
-        expected["bytes"] = b'41'
+        expected["bytes"] = b"41"
         expected["str"] = u"42"
 
     assert m.converting_constructors(inputs) == expected
@@ -255,7 +273,8 @@ def test_non_converting_constructors():
         with pytest.raises(TypeError) as excinfo:
             m.nonconverting_constructor(t, v)
         expected_error = "Object of type '{}' is not an instance of '{}'".format(
-            type(v).__name__, t)
+            type(v).__name__, t
+        )
         assert str(excinfo.value) == expected_error
 
 
@@ -263,12 +282,12 @@ def test_pybind11_str_raw_str():
     # specifically to exercise pybind11::str::raw_str
     cvt = m.convert_to_pybind11_str
     assert cvt(u"Str") == u"Str"
-    assert cvt(b'Bytes') == u"Bytes" if env.PY2 else "b'Bytes'"
+    assert cvt(b"Bytes") == u"Bytes" if env.PY2 else "b'Bytes'"
     assert cvt(None) == u"None"
     assert cvt(False) == u"False"
     assert cvt(True) == u"True"
     assert cvt(42) == u"42"
-    assert cvt(2**65) == u"36893488147419103232"
+    assert cvt(2 ** 65) == u"36893488147419103232"
     assert cvt(-1.50) == u"-1.5"
     assert cvt(()) == u"()"
     assert cvt((18,)) == u"(18,)"
@@ -283,29 +302,40 @@ def test_pybind11_str_raw_str():
     valid_utf8 = valid_orig.encode("utf-8")
     valid_cvt = cvt(valid_utf8)
     assert type(valid_cvt) == bytes  # Probably surprising.
-    assert valid_cvt == b'\xc7\xb1'
+    assert valid_cvt == b"\xc7\xb1"
 
-    malformed_utf8 = b'\x80'
+    malformed_utf8 = b"\x80"
     malformed_cvt = cvt(malformed_utf8)
     assert type(malformed_cvt) == bytes  # Probably surprising.
-    assert malformed_cvt == b'\x80'
+    assert malformed_cvt == b"\x80"
 
 
 def test_implicit_casting():
     """Tests implicit casting when assigning or appending to dicts and lists."""
     z = m.get_implicit_casting()
-    assert z['d'] == {
-        'char*_i1': 'abc', 'char*_i2': 'abc', 'char*_e': 'abc', 'char*_p': 'abc',
-        'str_i1': 'str', 'str_i2': 'str1', 'str_e': 'str2', 'str_p': 'str3',
-        'int_i1': 42, 'int_i2': 42, 'int_e': 43, 'int_p': 44
+    assert z["d"] == {
+        "char*_i1": "abc",
+        "char*_i2": "abc",
+        "char*_e": "abc",
+        "char*_p": "abc",
+        "str_i1": "str",
+        "str_i2": "str1",
+        "str_e": "str2",
+        "str_p": "str3",
+        "int_i1": 42,
+        "int_i2": 42,
+        "int_e": 43,
+        "int_p": 44,
     }
-    assert z['l'] == [3, 6, 9, 12, 15]
+    assert z["l"] == [3, 6, 9, 12, 15]
 
 
 def test_print(capture):
     with capture:
         m.print_function()
-    assert capture == """
+    assert (
+        capture
+        == """
         Hello, World!
         1 2.0 three True -- multiple args
         *args-and-a-custom-separator
@@ -313,14 +343,15 @@ def test_print(capture):
         flush
         py::print + str.format = this
     """
+    )
     assert capture.stderr == "this goes to stderr"
 
     with pytest.raises(RuntimeError) as excinfo:
         m.print_failure()
     assert str(excinfo.value) == "make_tuple(): unable to convert " + (
         "argument of type 'UnregisteredType' to Python object"
-        if debug_enabled else
-        "arguments to Python object (compile in debug mode for details)"
+        if debug_enabled
+        else "arguments to Python object (compile in debug mode for details)"
     )
 
 
@@ -342,8 +373,23 @@ def test_hash():
 
 def test_number_protocol():
     for a, b in [(1, 1), (3, 5)]:
-        li = [a == b, a != b, a < b, a <= b, a > b, a >= b, a + b,
-              a - b, a * b, a / b, a | b, a & b, a ^ b, a >> b, a << b]
+        li = [
+            a == b,
+            a != b,
+            a < b,
+            a <= b,
+            a > b,
+            a >= b,
+            a + b,
+            a - b,
+            a * b,
+            a / b,
+            a | b,
+            a & b,
+            a ^ b,
+            a >> b,
+            a << b,
+        ]
         assert m.test_number_protocol(a, b) == li
 
 
@@ -360,13 +406,16 @@ def test_issue2361():
     assert "'NoneType' object is not iterable" in str(excinfo.value)
 
 
-@pytest.mark.parametrize('method, args, fmt, expected_view', [
-    (m.test_memoryview_object, (b'red',), 'B', b'red'),
-    (m.test_memoryview_buffer_info, (b'green',), 'B', b'green'),
-    (m.test_memoryview_from_buffer, (False,), 'h', [3, 1, 4, 1, 5]),
-    (m.test_memoryview_from_buffer, (True,), 'H', [2, 7, 1, 8]),
-    (m.test_memoryview_from_buffer_nativeformat, (), '@i', [4, 7, 5]),
-])
+@pytest.mark.parametrize(
+    "method, args, fmt, expected_view",
+    [
+        (m.test_memoryview_object, (b"red",), "B", b"red"),
+        (m.test_memoryview_buffer_info, (b"green",), "B", b"green"),
+        (m.test_memoryview_from_buffer, (False,), "h", [3, 1, 4, 1, 5]),
+        (m.test_memoryview_from_buffer, (True,), "H", [2, 7, 1, 8]),
+        (m.test_memoryview_from_buffer_nativeformat, (), "@i", [4, 7, 5]),
+    ],
+)
 def test_memoryview(method, args, fmt, expected_view):
     view = method(*args)
     assert isinstance(view, memoryview)
@@ -380,12 +429,15 @@ def test_memoryview(method, args, fmt, expected_view):
 
 
 @pytest.mark.xfail("env.PYPY", reason="getrefcount is not available")
-@pytest.mark.parametrize('method', [
-    m.test_memoryview_object,
-    m.test_memoryview_buffer_info,
-])
+@pytest.mark.parametrize(
+    "method",
+    [
+        m.test_memoryview_object,
+        m.test_memoryview_buffer_info,
+    ],
+)
 def test_memoryview_refcount(method):
-    buf = b'\x0a\x0b\x0c\x0d'
+    buf = b"\x0a\x0b\x0c\x0d"
     ref_before = sys.getrefcount(buf)
     view = method(buf)
     ref_after = sys.getrefcount(buf)
@@ -396,13 +448,13 @@ def test_memoryview_refcount(method):
 def test_memoryview_from_buffer_empty_shape():
     view = m.test_memoryview_from_buffer_empty_shape()
     assert isinstance(view, memoryview)
-    assert view.format == 'B'
+    assert view.format == "B"
     if env.PY2:
         # Python 2 behavior is weird, but Python 3 (the future) is fine.
         # PyPy3 has <memoryview, while CPython 2 has <memory
-        assert bytes(view).startswith(b'<memory')
+        assert bytes(view).startswith(b"<memory")
     else:
-        assert bytes(view) == b''
+        assert bytes(view) == b""
 
 
 def test_test_memoryview_from_buffer_invalid_strides():
@@ -422,13 +474,15 @@ def test_test_memoryview_from_buffer_nullptr():
 def test_memoryview_from_memory():
     view = m.test_memoryview_from_memory()
     assert isinstance(view, memoryview)
-    assert view.format == 'B'
-    assert bytes(view) == b'\xff\xe1\xab\x37'
+    assert view.format == "B"
+    assert bytes(view) == b"\xff\xe1\xab\x37"
 
 
 def test_builtin_functions():
     assert m.get_len([i for i in range(42)]) == 42
     with pytest.raises(TypeError) as exc_info:
         m.get_len(i for i in range(42))
-    assert str(exc_info.value) in ["object of type 'generator' has no len()",
-                                   "'generator' has no length"]  # PyPy
+    assert str(exc_info.value) in [
+        "object of type 'generator' has no len()",
+        "'generator' has no length",
+    ]  # PyPy
diff --git a/tests/test_sequences_and_iterators.py b/tests/test_sequences_and_iterators.py
index 8f6c0c4bb..c3b608c43 100644
--- a/tests/test_sequences_and_iterators.py
+++ b/tests/test_sequences_and_iterators.py
@@ -10,7 +10,9 @@ def isclose(a, b, rel_tol=1e-05, abs_tol=0.0):
 
 
 def allclose(a_list, b_list, rel_tol=1e-05, abs_tol=0.0):
-    return all(isclose(a, b, rel_tol=rel_tol, abs_tol=abs_tol) for a, b in zip(a_list, b_list))
+    return all(
+        isclose(a, b, rel_tol=rel_tol, abs_tol=abs_tol) for a, b in zip(a_list, b_list)
+    )
 
 
 def test_generalized_iterators():
@@ -51,7 +53,7 @@ def test_sequence():
     cstats = ConstructorStats.get(m.Sequence)
 
     s = m.Sequence(5)
-    assert cstats.values() == ['of size', '5']
+    assert cstats.values() == ["of size", "5"]
 
     assert "Sequence" in repr(s)
     assert len(s) == 5
@@ -62,16 +64,16 @@ def test_sequence():
     assert isclose(s[0], 12.34) and isclose(s[3], 56.78)
 
     rev = reversed(s)
-    assert cstats.values() == ['of size', '5']
+    assert cstats.values() == ["of size", "5"]
 
     rev2 = s[::-1]
-    assert cstats.values() == ['of size', '5']
+    assert cstats.values() == ["of size", "5"]
 
     it = iter(m.Sequence(0))
     for _ in range(3):  # __next__ must continue to raise StopIteration
         with pytest.raises(StopIteration):
             next(it)
-    assert cstats.values() == ['of size', '0']
+    assert cstats.values() == ["of size", "0"]
 
     expected = [0, 56.78, 0, 0, 12.34]
     assert allclose(rev, expected)
@@ -79,7 +81,7 @@ def test_sequence():
     assert rev == rev2
 
     rev[0::2] = m.Sequence([2.0, 2.0, 2.0])
-    assert cstats.values() == ['of size', '3', 'from std::vector']
+    assert cstats.values() == ["of size", "3", "from std::vector"]
 
     assert allclose(rev, [2, 56.78, 2, 0, 2])
 
@@ -103,10 +105,11 @@ def test_sequence():
 
 def test_sequence_length():
     """#2076: Exception raised by len(arg) should be propagated """
+
     class BadLen(RuntimeError):
         pass
 
-    class SequenceLike():
+    class SequenceLike:
         def __getitem__(self, i):
             return None
 
@@ -121,17 +124,17 @@ def test_sequence_length():
 
 
 def test_map_iterator():
-    sm = m.StringMap({'hi': 'bye', 'black': 'white'})
-    assert sm['hi'] == 'bye'
+    sm = m.StringMap({"hi": "bye", "black": "white"})
+    assert sm["hi"] == "bye"
     assert len(sm) == 2
-    assert sm['black'] == 'white'
+    assert sm["black"] == "white"
 
     with pytest.raises(KeyError):
-        assert sm['orange']
-    sm['orange'] = 'banana'
-    assert sm['orange'] == 'banana'
+        assert sm["orange"]
+    sm["orange"] = "banana"
+    assert sm["orange"] == "banana"
 
-    expected = {'hi': 'bye', 'black': 'white', 'orange': 'banana'}
+    expected = {"hi": "bye", "black": "white", "orange": "banana"}
     for k in sm:
         assert sm[k] == expected[k]
     for k, v in sm.items():
@@ -179,7 +182,8 @@ def test_iterator_passthrough():
     """#181: iterator passthrough did not compile"""
     from pybind11_tests.sequences_and_iterators import iterator_passthrough
 
-    assert list(iterator_passthrough(iter([3, 5, 7, 9, 11, 13, 15]))) == [3, 5, 7, 9, 11, 13, 15]
+    values = [3, 5, 7, 9, 11, 13, 15]
+    assert list(iterator_passthrough(iter(values))) == values
 
 
 def test_iterator_rvp():
diff --git a/tests/test_smart_ptr.py b/tests/test_smart_ptr.py
index 0b1ca45b5..c55bffba0 100644
--- a/tests/test_smart_ptr.py
+++ b/tests/test_smart_ptr.py
@@ -7,7 +7,9 @@ from pybind11_tests import ConstructorStats  # noqa: E402
 
 def test_smart_ptr(capture):
     # Object1
-    for i, o in enumerate([m.make_object_1(), m.make_object_2(), m.MyObject1(3)], start=1):
+    for i, o in enumerate(
+        [m.make_object_1(), m.make_object_2(), m.MyObject1(3)], start=1
+    ):
         assert o.getRefCount() == 1
         with capture:
             m.print_object_1(o)
@@ -16,8 +18,9 @@ def test_smart_ptr(capture):
             m.print_object_4(o)
         assert capture == "MyObject1[{i}]\n".format(i=i) * 4
 
-    for i, o in enumerate([m.make_myobject1_1(), m.make_myobject1_2(), m.MyObject1(6), 7],
-                          start=4):
+    for i, o in enumerate(
+        [m.make_myobject1_1(), m.make_myobject1_2(), m.MyObject1(6), 7], start=4
+    ):
         print(o)
         with capture:
             if not isinstance(o, int):
@@ -29,11 +32,15 @@ def test_smart_ptr(capture):
             m.print_myobject1_2(o)
             m.print_myobject1_3(o)
             m.print_myobject1_4(o)
-        assert capture == "MyObject1[{i}]\n".format(i=i) * (4 if isinstance(o, int) else 8)
+
+        times = 4 if isinstance(o, int) else 8
+        assert capture == "MyObject1[{i}]\n".format(i=i) * times
 
     cstats = ConstructorStats.get(m.MyObject1)
     assert cstats.alive() == 0
-    expected_values = ['MyObject1[{}]'.format(i) for i in range(1, 7)] + ['MyObject1[7]'] * 4
+    expected_values = ["MyObject1[{}]".format(i) for i in range(1, 7)] + [
+        "MyObject1[7]"
+    ] * 4
     assert cstats.values() == expected_values
     assert cstats.default_constructions == 0
     assert cstats.copy_constructions == 0
@@ -42,7 +49,9 @@ def test_smart_ptr(capture):
     assert cstats.move_assignments == 0
 
     # Object2
-    for i, o in zip([8, 6, 7], [m.MyObject2(8), m.make_myobject2_1(), m.make_myobject2_2()]):
+    for i, o in zip(
+        [8, 6, 7], [m.MyObject2(8), m.make_myobject2_1(), m.make_myobject2_2()]
+    ):
         print(o)
         with capture:
             m.print_myobject2_1(o)
@@ -55,7 +64,7 @@ def test_smart_ptr(capture):
     assert cstats.alive() == 1
     o = None
     assert cstats.alive() == 0
-    assert cstats.values() == ['MyObject2[8]', 'MyObject2[6]', 'MyObject2[7]']
+    assert cstats.values() == ["MyObject2[8]", "MyObject2[6]", "MyObject2[7]"]
     assert cstats.default_constructions == 0
     assert cstats.copy_constructions == 0
     # assert cstats.move_constructions >= 0 # Doesn't invoke any
@@ -63,7 +72,9 @@ def test_smart_ptr(capture):
     assert cstats.move_assignments == 0
 
     # Object3
-    for i, o in zip([9, 8, 9], [m.MyObject3(9), m.make_myobject3_1(), m.make_myobject3_2()]):
+    for i, o in zip(
+        [9, 8, 9], [m.MyObject3(9), m.make_myobject3_1(), m.make_myobject3_2()]
+    ):
         print(o)
         with capture:
             m.print_myobject3_1(o)
@@ -76,7 +87,7 @@ def test_smart_ptr(capture):
     assert cstats.alive() == 1
     o = None
     assert cstats.alive() == 0
-    assert cstats.values() == ['MyObject3[9]', 'MyObject3[8]', 'MyObject3[9]']
+    assert cstats.values() == ["MyObject3[9]", "MyObject3[8]", "MyObject3[9]"]
     assert cstats.default_constructions == 0
     assert cstats.copy_constructions == 0
     # assert cstats.move_constructions >= 0 # Doesn't invoke any
@@ -96,7 +107,7 @@ def test_smart_ptr(capture):
     # ref<>
     cstats = m.cstats_ref()
     assert cstats.alive() == 0
-    assert cstats.values() == ['from pointer'] * 10
+    assert cstats.values() == ["from pointer"] * 10
     assert cstats.default_constructions == 30
     assert cstats.copy_constructions == 12
     # assert cstats.move_constructions >= 0 # Doesn't invoke any
@@ -186,7 +197,9 @@ def test_shared_ptr_from_this_and_references():
     ref = s.ref  # init_holder_helper(holder_ptr=false, owned=false, bad_wp=false)
     assert stats.alive() == 2
     assert s.set_ref(ref)
-    assert s.set_holder(ref)  # std::enable_shared_from_this can create a holder from a reference
+    assert s.set_holder(
+        ref
+    )  # std::enable_shared_from_this can create a holder from a reference
 
     bad_wp = s.bad_wp  # init_holder_helper(holder_ptr=false, owned=false, bad_wp=true)
     assert stats.alive() == 2
@@ -200,12 +213,16 @@ def test_shared_ptr_from_this_and_references():
     assert s.set_ref(copy)
     assert s.set_holder(copy)
 
-    holder_ref = s.holder_ref  # init_holder_helper(holder_ptr=true, owned=false, bad_wp=false)
+    holder_ref = (
+        s.holder_ref
+    )  # init_holder_helper(holder_ptr=true, owned=false, bad_wp=false)
     assert stats.alive() == 3
     assert s.set_ref(holder_ref)
     assert s.set_holder(holder_ref)
 
-    holder_copy = s.holder_copy  # init_holder_helper(holder_ptr=true, owned=true, bad_wp=false)
+    holder_copy = (
+        s.holder_copy
+    )  # init_holder_helper(holder_ptr=true, owned=true, bad_wp=false)
     assert stats.alive() == 3
     assert s.set_ref(holder_copy)
     assert s.set_holder(holder_copy)
@@ -277,8 +294,10 @@ def test_smart_ptr_from_default():
     instance = m.HeldByDefaultHolder()
     with pytest.raises(RuntimeError) as excinfo:
         m.HeldByDefaultHolder.load_shared_ptr(instance)
-    assert "Unable to load a custom holder type from a " \
-           "default-holder instance" in str(excinfo.value)
+    assert (
+        "Unable to load a custom holder type from a "
+        "default-holder instance" in str(excinfo.value)
+    )
 
 
 def test_shared_ptr_gc():
diff --git a/tests/test_stl.py b/tests/test_stl.py
index 141b3e849..330017544 100644
--- a/tests/test_stl.py
+++ b/tests/test_stl.py
@@ -88,7 +88,7 @@ def test_recursive_casting():
     assert m.cast_rv_nested() == [[[{"b": "rvalue", "c": "rvalue"}], [{"a": "rvalue"}]]]
     assert m.cast_lv_nested() == {
         "a": [[["lvalue", "lvalue"]], [["lvalue", "lvalue"]]],
-        "b": [[["lvalue", "lvalue"], ["lvalue", "lvalue"]]]
+        "b": [[["lvalue", "lvalue"], ["lvalue", "lvalue"]]],
     }
 
     # Issue #853 test case:
@@ -106,15 +106,15 @@ def test_move_out_container():
     assert [x.value for x in moved_out_list] == [0, 1, 2]
 
 
-@pytest.mark.skipif(not hasattr(m, "has_optional"), reason='no <optional>')
+@pytest.mark.skipif(not hasattr(m, "has_optional"), reason="no <optional>")
 def test_optional():
     assert m.double_or_zero(None) == 0
     assert m.double_or_zero(42) == 84
-    pytest.raises(TypeError, m.double_or_zero, 'foo')
+    pytest.raises(TypeError, m.double_or_zero, "foo")
 
     assert m.half_or_none(0) is None
     assert m.half_or_none(42) == 21
-    pytest.raises(TypeError, m.half_or_none, 'foo')
+    pytest.raises(TypeError, m.half_or_none, "foo")
 
     assert m.test_nullopt() == 42
     assert m.test_nullopt(None) == 42
@@ -134,15 +134,17 @@ def test_optional():
     assert holder.member_initialized()
 
 
-@pytest.mark.skipif(not hasattr(m, "has_exp_optional"), reason='no <experimental/optional>')
+@pytest.mark.skipif(
+    not hasattr(m, "has_exp_optional"), reason="no <experimental/optional>"
+)
 def test_exp_optional():
     assert m.double_or_zero_exp(None) == 0
     assert m.double_or_zero_exp(42) == 84
-    pytest.raises(TypeError, m.double_or_zero_exp, 'foo')
+    pytest.raises(TypeError, m.double_or_zero_exp, "foo")
 
     assert m.half_or_none_exp(0) is None
     assert m.half_or_none_exp(42) == 21
-    pytest.raises(TypeError, m.half_or_none_exp, 'foo')
+    pytest.raises(TypeError, m.half_or_none_exp, "foo")
 
     assert m.test_nullopt_exp() == 42
     assert m.test_nullopt_exp(None) == 42
@@ -160,7 +162,7 @@ def test_exp_optional():
     assert holder.member_initialized()
 
 
-@pytest.mark.skipif(not hasattr(m, "load_variant"), reason='no <variant>')
+@pytest.mark.skipif(not hasattr(m, "load_variant"), reason="no <variant>")
 def test_variant(doc):
     assert m.load_variant(1) == "int"
     assert m.load_variant("1") == "std::string"
@@ -172,34 +174,44 @@ def test_variant(doc):
 
     assert m.cast_variant() == (5, "Hello")
 
-    assert doc(m.load_variant) == "load_variant(arg0: Union[int, str, float, None]) -> str"
+    assert (
+        doc(m.load_variant) == "load_variant(arg0: Union[int, str, float, None]) -> str"
+    )
 
 
 def test_vec_of_reference_wrapper():
     """#171: Can't return reference wrappers (or STL structures containing them)"""
-    assert str(m.return_vec_of_reference_wrapper(UserType(4))) == \
-        "[UserType(1), UserType(2), UserType(3), UserType(4)]"
+    assert (
+        str(m.return_vec_of_reference_wrapper(UserType(4)))
+        == "[UserType(1), UserType(2), UserType(3), UserType(4)]"
+    )
 
 
 def test_stl_pass_by_pointer(msg):
     """Passing nullptr or None to an STL container pointer is not expected to work"""
     with pytest.raises(TypeError) as excinfo:
         m.stl_pass_by_pointer()  # default value is `nullptr`
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         stl_pass_by_pointer(): incompatible function arguments. The following argument types are supported:
             1. (v: List[int] = None) -> List[int]
 
         Invoked with:
     """  # noqa: E501 line too long
+    )
 
     with pytest.raises(TypeError) as excinfo:
         m.stl_pass_by_pointer(None)
-    assert msg(excinfo.value) == """
+    assert (
+        msg(excinfo.value)
+        == """
         stl_pass_by_pointer(): incompatible function arguments. The following argument types are supported:
             1. (v: List[int] = None) -> List[int]
 
         Invoked with: None
     """  # noqa: E501 line too long
+    )
 
     assert m.stl_pass_by_pointer([1, 2, 3]) == [1, 2, 3]
 
@@ -209,10 +221,12 @@ def test_missing_header_message():
     <pybind11/stl.h> should result in a helpful suggestion in the error message"""
     import pybind11_cross_module_tests as cm
 
-    expected_message = ("Did you forget to `#include <pybind11/stl.h>`? Or <pybind11/complex.h>,\n"
-                        "<pybind11/functional.h>, <pybind11/chrono.h>, etc. Some automatic\n"
-                        "conversions are optional and require extra headers to be included\n"
-                        "when compiling your pybind11 module.")
+    expected_message = (
+        "Did you forget to `#include <pybind11/stl.h>`? Or <pybind11/complex.h>,\n"
+        "<pybind11/functional.h>, <pybind11/chrono.h>, etc. Some automatic\n"
+        "conversions are optional and require extra headers to be included\n"
+        "when compiling your pybind11 module."
+    )
 
     with pytest.raises(TypeError) as excinfo:
         cm.missing_header_arg([1.0, 2.0, 3.0])
@@ -226,9 +240,9 @@ def test_missing_header_message():
 def test_function_with_string_and_vector_string_arg():
     """Check if a string is NOT implicitly converted to a list, which was the
     behavior before fix of issue #1258"""
-    assert m.func_with_string_or_vector_string_arg_overload(('A', 'B', )) == 2
-    assert m.func_with_string_or_vector_string_arg_overload(['A', 'B']) == 2
-    assert m.func_with_string_or_vector_string_arg_overload('A') == 3
+    assert m.func_with_string_or_vector_string_arg_overload(("A", "B")) == 2
+    assert m.func_with_string_or_vector_string_arg_overload(["A", "B"]) == 2
+    assert m.func_with_string_or_vector_string_arg_overload("A") == 3
 
 
 def test_stl_ownership():
@@ -247,6 +261,6 @@ def test_array_cast_sequence():
 def test_issue_1561():
     """ check fix for issue #1561 """
     bar = m.Issue1561Outer()
-    bar.list = [m.Issue1561Inner('bar')]
+    bar.list = [m.Issue1561Inner("bar")]
     bar.list
-    assert bar.list[0].data == 'bar'
+    assert bar.list[0].data == "bar"
diff --git a/tests/test_stl_binders.py b/tests/test_stl_binders.py
index f9b8ea4af..84132a2b4 100644
--- a/tests/test_stl_binders.py
+++ b/tests/test_stl_binders.py
@@ -45,7 +45,7 @@ def test_vector_int():
 
     # test error handling, and that the vector is unchanged
     with pytest.raises(RuntimeError):
-        v_int2.extend([8, 'a'])
+        v_int2.extend([8, "a"])
 
     assert v_int2 == m.VectorInt([0, 99, 2, 3, 4, 5, 6, 7])
 
@@ -79,8 +79,8 @@ def test_vector_buffer():
         assert mv[2] == 5
         mv[2] = 6
     else:
-        assert mv[2] == '\x05'
-        mv[2] = '\x06'
+        assert mv[2] == "\x05"
+        mv[2] = "\x06"
     assert v[2] == 6
 
     if not env.PY2:
@@ -114,11 +114,17 @@ def test_vector_buffer_numpy():
     v = m.get_vectorstruct()
     assert v[0].x == 5
     ma = np.asarray(v)
-    ma[1]['x'] = 99
+    ma[1]["x"] = 99
     assert v[1].x == 99
 
-    v = m.VectorStruct(np.zeros(3, dtype=np.dtype([('w', 'bool'), ('x', 'I'),
-                                                   ('y', 'float64'), ('z', 'bool')], align=True)))
+    v = m.VectorStruct(
+        np.zeros(
+            3,
+            dtype=np.dtype(
+                [("w", "bool"), ("x", "I"), ("y", "float64"), ("z", "bool")], align=True
+            ),
+        )
+    )
     assert len(v) == 3
 
     b = np.array([1, 2, 3, 4], dtype=np.uint8)
@@ -151,31 +157,31 @@ def test_vector_custom():
 
 def test_map_string_double():
     mm = m.MapStringDouble()
-    mm['a'] = 1
-    mm['b'] = 2.5
+    mm["a"] = 1
+    mm["b"] = 2.5
 
-    assert list(mm) == ['a', 'b']
-    assert list(mm.items()) == [('a', 1), ('b', 2.5)]
+    assert list(mm) == ["a", "b"]
+    assert list(mm.items()) == [("a", 1), ("b", 2.5)]
     assert str(mm) == "MapStringDouble{a: 1, b: 2.5}"
 
     um = m.UnorderedMapStringDouble()
-    um['ua'] = 1.1
-    um['ub'] = 2.6
+    um["ua"] = 1.1
+    um["ub"] = 2.6
 
-    assert sorted(list(um)) == ['ua', 'ub']
-    assert sorted(list(um.items())) == [('ua', 1.1), ('ub', 2.6)]
+    assert sorted(list(um)) == ["ua", "ub"]
+    assert sorted(list(um.items())) == [("ua", 1.1), ("ub", 2.6)]
     assert "UnorderedMapStringDouble" in str(um)
 
 
 def test_map_string_double_const():
     mc = m.MapStringDoubleConst()
-    mc['a'] = 10
-    mc['b'] = 20.5
+    mc["a"] = 10
+    mc["b"] = 20.5
     assert str(mc) == "MapStringDoubleConst{a: 10, b: 20.5}"
 
     umc = m.UnorderedMapStringDoubleConst()
-    umc['a'] = 11
-    umc['b'] = 21.5
+    umc["a"] = 11
+    umc["b"] = 21.5
 
     str(umc)
 
@@ -196,7 +202,7 @@ def test_noncopyable_containers():
 
     i = 1
     for j in dnc:
-        assert(j.value == i)
+        assert j.value == i
         i += 1
 
     # std::map
@@ -265,21 +271,21 @@ def test_noncopyable_containers():
 
 def test_map_delitem():
     mm = m.MapStringDouble()
-    mm['a'] = 1
-    mm['b'] = 2.5
+    mm["a"] = 1
+    mm["b"] = 2.5
 
-    assert list(mm) == ['a', 'b']
-    assert list(mm.items()) == [('a', 1), ('b', 2.5)]
-    del mm['a']
-    assert list(mm) == ['b']
-    assert list(mm.items()) == [('b', 2.5)]
+    assert list(mm) == ["a", "b"]
+    assert list(mm.items()) == [("a", 1), ("b", 2.5)]
+    del mm["a"]
+    assert list(mm) == ["b"]
+    assert list(mm.items()) == [("b", 2.5)]
 
     um = m.UnorderedMapStringDouble()
-    um['ua'] = 1.1
-    um['ub'] = 2.6
+    um["ua"] = 1.1
+    um["ub"] = 2.6
 
-    assert sorted(list(um)) == ['ua', 'ub']
-    assert sorted(list(um.items())) == [('ua', 1.1), ('ub', 2.6)]
-    del um['ua']
-    assert sorted(list(um)) == ['ub']
-    assert sorted(list(um.items())) == [('ub', 2.6)]
+    assert sorted(list(um)) == ["ua", "ub"]
+    assert sorted(list(um.items())) == [("ua", 1.1), ("ub", 2.6)]
+    del um["ua"]
+    assert sorted(list(um)) == ["ub"]
+    assert sorted(list(um.items())) == [("ub", 2.6)]
diff --git a/tests/test_tagbased_polymorphic.py b/tests/test_tagbased_polymorphic.py
index 94f374da9..64eb8a3c1 100644
--- a/tests/test_tagbased_polymorphic.py
+++ b/tests/test_tagbased_polymorphic.py
@@ -5,16 +5,24 @@ from pybind11_tests import tagbased_polymorphic as m
 def test_downcast():
     zoo = m.create_zoo()
     assert [type(animal) for animal in zoo] == [
-        m.Labrador, m.Dog, m.Chihuahua, m.Cat, m.Panther
+        m.Labrador,
+        m.Dog,
+        m.Chihuahua,
+        m.Cat,
+        m.Panther,
     ]
     assert [animal.name for animal in zoo] == [
-        "Fido", "Ginger", "Hertzl", "Tiger", "Leo"
+        "Fido",
+        "Ginger",
+        "Hertzl",
+        "Tiger",
+        "Leo",
     ]
     zoo[1].sound = "woooooo"
     assert [dog.bark() for dog in zoo[:3]] == [
         "Labrador Fido goes WOOF!",
         "Dog Ginger goes woooooo",
-        "Chihuahua Hertzl goes iyiyiyiyiyi and runs in circles"
+        "Chihuahua Hertzl goes iyiyiyiyiyi and runs in circles",
     ]
     assert [cat.purr() for cat in zoo[3:]] == ["mrowr", "mrrrRRRRRR"]
     zoo[0].excitement -= 1000
diff --git a/tests/test_virtual_functions.py b/tests/test_virtual_functions.py
index 53bcfd120..ae1993016 100644
--- a/tests/test_virtual_functions.py
+++ b/tests/test_virtual_functions.py
@@ -14,18 +14,18 @@ def test_override(capture, msg):
             self.data = "Hello world"
 
         def run(self, value):
-            print('ExtendedExampleVirt::run(%i), calling parent..' % value)
+            print("ExtendedExampleVirt::run(%i), calling parent.." % value)
             return super(ExtendedExampleVirt, self).run(value + 1)
 
         def run_bool(self):
-            print('ExtendedExampleVirt::run_bool()')
+            print("ExtendedExampleVirt::run_bool()")
             return False
 
         def get_string1(self):
             return "override1"
 
         def pure_virtual(self):
-            print('ExtendedExampleVirt::pure_virtual(): %s' % self.data)
+            print("ExtendedExampleVirt::pure_virtual(): %s" % self.data)
 
     class ExtendedExampleVirt2(ExtendedExampleVirt):
         def __init__(self, state):
@@ -37,21 +37,30 @@ def test_override(capture, msg):
     ex12 = m.ExampleVirt(10)
     with capture:
         assert m.runExampleVirt(ex12, 20) == 30
-    assert capture == """
+    assert (
+        capture
+        == """
         Original implementation of ExampleVirt::run(state=10, value=20, str1=default1, str2=default2)
     """  # noqa: E501 line too long
+    )
 
     with pytest.raises(RuntimeError) as excinfo:
         m.runExampleVirtVirtual(ex12)
-    assert msg(excinfo.value) == 'Tried to call pure virtual function "ExampleVirt::pure_virtual"'
+    assert (
+        msg(excinfo.value)
+        == 'Tried to call pure virtual function "ExampleVirt::pure_virtual"'
+    )
 
     ex12p = ExtendedExampleVirt(10)
     with capture:
         assert m.runExampleVirt(ex12p, 20) == 32
-    assert capture == """
+    assert (
+        capture
+        == """
         ExtendedExampleVirt::run(20), calling parent..
         Original implementation of ExampleVirt::run(state=11, value=21, str1=override1, str2=default2)
     """  # noqa: E501 line too long
+    )
     with capture:
         assert m.runExampleVirtBool(ex12p) is False
     assert capture == "ExtendedExampleVirt::run_bool()"
@@ -62,16 +71,19 @@ def test_override(capture, msg):
     ex12p2 = ExtendedExampleVirt2(15)
     with capture:
         assert m.runExampleVirt(ex12p2, 50) == 68
-    assert capture == """
+    assert (
+        capture
+        == """
         ExtendedExampleVirt::run(50), calling parent..
         Original implementation of ExampleVirt::run(state=17, value=51, str1=override1, str2=override2)
     """  # noqa: E501 line too long
+    )
 
     cstats = ConstructorStats.get(m.ExampleVirt)
     assert cstats.alive() == 3
     del ex12, ex12p, ex12p2
     assert cstats.alive() == 0
-    assert cstats.values() == ['10', '11', '17']
+    assert cstats.values() == ["10", "11", "17"]
     assert cstats.copy_constructions == 0
     assert cstats.move_constructions >= 0
 
@@ -82,6 +94,7 @@ def test_alias_delay_initialization1(capture):
     If we just create and use an A instance directly, the trampoline initialization is
     bypassed and we only initialize an A() instead (for performance reasons).
     """
+
     class B(m.A):
         def __init__(self):
             super(B, self).__init__()
@@ -103,12 +116,15 @@ def test_alias_delay_initialization1(capture):
         m.call_f(b)
         del b
         pytest.gc_collect()
-    assert capture == """
+    assert (
+        capture
+        == """
         PyA.PyA()
         PyA.f()
         In python f()
         PyA.~PyA()
     """
+    )
 
 
 def test_alias_delay_initialization2(capture):
@@ -118,6 +134,7 @@ def test_alias_delay_initialization2(capture):
     performance penalty, it also allows us to do more things with the trampoline
     class such as defining local variables and performing construction/destruction.
     """
+
     class B2(m.A2):
         def __init__(self):
             super(B2, self).__init__()
@@ -135,7 +152,9 @@ def test_alias_delay_initialization2(capture):
         m.call_f(a3)
         del a3
         pytest.gc_collect()
-    assert capture == """
+    assert (
+        capture
+        == """
         PyA2.PyA2()
         PyA2.f()
         A2.f()
@@ -145,6 +164,7 @@ def test_alias_delay_initialization2(capture):
         A2.f()
         PyA2.~PyA2()
     """
+    )
 
     # Python subclass version
     with capture:
@@ -152,20 +172,22 @@ def test_alias_delay_initialization2(capture):
         m.call_f(b2)
         del b2
         pytest.gc_collect()
-    assert capture == """
+    assert (
+        capture
+        == """
         PyA2.PyA2()
         PyA2.f()
         In python B2.f()
         PyA2.~PyA2()
     """
+    )
 
 
 # PyPy: Reference count > 1 causes call with noncopyable instance
 # to fail in ncv1.print_nc()
 @pytest.mark.xfail("env.PYPY")
 @pytest.mark.skipif(
-    not hasattr(m, "NCVirt"),
-    reason="NCVirt does not work on Intel/PGI/NVCC compilers"
+    not hasattr(m, "NCVirt"), reason="NCVirt does not work on Intel/PGI/NVCC compilers"
 )
 def test_move_support():
     class NCVirtExt(m.NCVirt):
@@ -205,8 +227,8 @@ def test_move_support():
     del ncv1, ncv2
     assert nc_stats.alive() == 0
     assert mv_stats.alive() == 0
-    assert nc_stats.values() == ['4', '9', '9', '9']
-    assert mv_stats.values() == ['4', '5', '7', '7']
+    assert nc_stats.values() == ["4", "9", "9", "9"]
+    assert mv_stats.values() == ["4", "5", "7", "7"]
     assert nc_stats.copy_constructions == 0
     assert mv_stats.copy_constructions == 1
     assert nc_stats.move_constructions >= 0
@@ -215,6 +237,7 @@ def test_move_support():
 
 def test_dispatch_issue(msg):
     """#159: virtual function dispatch has problems with similar-named functions"""
+
     class PyClass1(m.DispatchIssue):
         def dispatch(self):
             return "Yay.."
@@ -223,7 +246,10 @@ def test_dispatch_issue(msg):
         def dispatch(self):
             with pytest.raises(RuntimeError) as excinfo:
                 super(PyClass2, self).dispatch()
-            assert msg(excinfo.value) == 'Tried to call pure virtual function "Base::dispatch"'
+            assert (
+                msg(excinfo.value)
+                == 'Tried to call pure virtual function "Base::dispatch"'
+            )
 
             p = PyClass1()
             return m.dispatch_issue_go(p)
@@ -339,7 +365,7 @@ def test_inherited_virtuals():
 
     class DT(m.D_Tpl):
         def say_something(self, times):
-            return "DT says:" + (' quack' * times)
+            return "DT says:" + (" quack" * times)
 
         def unlucky_number(self):
             return 1234
@@ -355,7 +381,7 @@ def test_inherited_virtuals():
 
     class DT2(DT):
         def say_something(self, times):
-            return "DT2: " + ('QUACK' * times)
+            return "DT2: " + ("QUACK" * times)
 
         def unlucky_number(self):
             return -3