Minor pytest maintenance (#702)

* Add `pytest.ini` config file and set default options there instead of
  in `CMakeLists.txt` (command line arguments).

* Change all output capture from `capfd` (filedescriptors) to `capsys`
  (Python's `sys.stdout` and `sys.stderr`). This avoids capturing
  low-level C errors, e.g. from the debug build of Python.

* Set pytest minimum version to 3.0 to make it easier to use new
  features. Removed conditional use of `excinfo.match()`.

* Clean up some leftover function-level `@pytest.requires_numpy`.

tests/CMakeLists.txt

@@ -150,16 +150,20 @@ endif()
 
 # Make sure pytest is found or produce a fatal error
 if(NOT PYBIND11_PYTEST_FOUND)
-  execute_process(COMMAND ${PYTHON_EXECUTABLE} -c "import pytest" OUTPUT_QUIET ERROR_QUIET
-                  RESULT_VARIABLE PYBIND11_EXEC_PYTHON_ERR)
-  if(PYBIND11_EXEC_PYTHON_ERR)
-    message(FATAL_ERROR "Running the tests requires pytest.  Please install it manually (try: ${PYTHON_EXECUTABLE} -m pip install pytest)")
+  execute_process(COMMAND ${PYTHON_EXECUTABLE} -c "import pytest; print(pytest.__version__)"
+                  RESULT_VARIABLE pytest_not_found OUTPUT_VARIABLE pytest_version ERROR_QUIET)
+  if(pytest_not_found)
+    message(FATAL_ERROR "Running the tests requires pytest. Please install it manually"
+                        " (try: ${PYTHON_EXECUTABLE} -m pip install pytest)")
+  elseif(pytest_version VERSION_LESS 3.0)
+    message(FATAL_ERROR "Running the tests requires pytest >= 3.0. Found: ${pytest_version}"
+                        "Please update it (try: ${PYTHON_EXECUTABLE} -m pip install -U pytest)")
   endif()
   set(PYBIND11_PYTEST_FOUND TRUE CACHE INTERNAL "")
 endif()
 
 # A single command to compile and run the tests
-add_custom_target(pytest COMMAND ${PYTHON_EXECUTABLE} -m pytest -rws --capture=sys ${PYBIND11_PYTEST_FILES}
+add_custom_target(pytest COMMAND ${PYTHON_EXECUTABLE} -m pytest ${PYBIND11_PYTEST_FILES}
                   DEPENDS pybind11_tests WORKING_DIRECTORY ${testdir})
 
 if(PYBIND11_TEST_OVERRIDE)

tests/conftest.py

@@ -103,9 +103,9 @@ class Capture(object):
 
 
 @pytest.fixture
-def capture(capfd):
-    """Extended `capfd` with context manager and custom equality operators"""
-    return Capture(capfd)
+def capture(capsys):
+    """Extended `capsys` with context manager and custom equality operators"""
+    return Capture(capsys)
 
 
 class SanitizedString(object):

tests/pytest.ini

@@ -0,0 +1,7 @@
+[pytest]
+minversion = 3.0
+addopts =
+    # show summary of skipped tests
+    -rs
+    # capture only Python print and C++ py::print, but not C output (low-level Python errors)
+    --capture=sys

tests/test_buffers.py

@@ -1,11 +1,12 @@
 import pytest
 from pybind11_tests import Matrix, ConstructorStats
 
+pytestmark = pytest.requires_numpy
+
 with pytest.suppress(ImportError):
     import numpy as np
 
 
-@pytest.requires_numpy
 def test_from_python():
     with pytest.raises(RuntimeError) as excinfo:
         Matrix(np.array([1, 2, 3]))  # trying to assign a 1D array
@@ -32,7 +33,6 @@ def test_from_python():
 # PyPy: Memory leak in the "np.array(m, copy=False)" call
 # https://bitbucket.org/pypy/pypy/issues/2444
 @pytest.unsupported_on_pypy
-@pytest.requires_numpy
 def test_to_python():
     m = Matrix(5, 5)
 

tests/test_kwargs_and_defaults.py

@@ -34,10 +34,8 @@ def test_named_arguments(msg):
     with pytest.raises(TypeError) as excinfo:
         # noinspection PyArgumentList
         kw_func2(x=5, y=10, z=12)
-    if hasattr(excinfo, "match"):  # (pytest <3.0 doesn't have `.match()`)
-        assert excinfo.match(
-            r'(?s)^kw_func2\(\): incompatible.*Invoked with: kwargs: ((x=5|y=10|z=12)(, |$))' +
-            '{3}$')
+    assert excinfo.match(
+        r'(?s)^kw_func2\(\): incompatible.*Invoked with: kwargs: ((x=5|y=10|z=12)(, |$))' + '{3}$')
 
     assert kw_func4() == "{13 17}"
     assert kw_func4(myList=[1, 2, 3]) == "{1 2 3}"