diff --git a/tests/test_multiple_inheritance.cpp b/tests/test_multiple_inheritance.cpp
index 2fbe11278..c52b991aa 100644
--- a/tests/test_multiple_inheritance.cpp
+++ b/tests/test_multiple_inheritance.cpp
@@ -11,47 +11,74 @@
 #include "pybind11_tests.h"
 #include "constructor_stats.h"
 
-struct Base1 {
-    Base1(int i) : i(i) { }
-    int foo() { return i; }
-    int i;
-};
-
-struct Base2 {
-    Base2(int i) : i(i) { }
-    int bar() { return i; }
-    int i;
-};
-
+// Many bases for testing that multiple inheritance from many classes (i.e. requiring extra
+// space for holder constructed flags) works.
 template <int N> struct BaseN {
     BaseN(int i) : i(i) { }
     int i;
 };
 
-struct Base12 : Base1, Base2 {
-    Base12(int i, int j) : Base1(i), Base2(j) { }
+// test_mi_static_properties
+struct Vanilla {
+    std::string vanilla() { return "Vanilla"; };
 };
-
-struct MIType : Base12 {
-    MIType(int i, int j) : Base12(i, j) { }
+struct WithStatic1 {
+    static std::string static_func1() { return "WithStatic1"; };
+    static int static_value1;
 };
+struct WithStatic2 {
+    static std::string static_func2() { return "WithStatic2"; };
+    static int static_value2;
+};
+struct VanillaStaticMix1 : Vanilla, WithStatic1, WithStatic2 {
+    static std::string static_func() { return "VanillaStaticMix1"; }
+    static int static_value;
+};
+struct VanillaStaticMix2 : WithStatic1, Vanilla, WithStatic2 {
+    static std::string static_func() { return "VanillaStaticMix2"; }
+    static int static_value;
+};
+int WithStatic1::static_value1 = 1;
+int WithStatic2::static_value2 = 2;
+int VanillaStaticMix1::static_value = 12;
+int VanillaStaticMix2::static_value = 12;
 
-test_initializer multiple_inheritance([](py::module &m) {
+TEST_SUBMODULE(multiple_inheritance, m) {
+
+    // test_multiple_inheritance_mix1
+    // test_multiple_inheritance_mix2
+    struct Base1 {
+        Base1(int i) : i(i) { }
+        int foo() { return i; }
+        int i;
+    };
     py::class_<Base1> b1(m, "Base1");
     b1.def(py::init<int>())
       .def("foo", &Base1::foo);
 
+    struct Base2 {
+        Base2(int i) : i(i) { }
+        int bar() { return i; }
+        int i;
+    };
     py::class_<Base2> b2(m, "Base2");
     b2.def(py::init<int>())
       .def("bar", &Base2::bar);
 
-    py::class_<Base12, Base1, Base2>(m, "Base12");
 
+    // test_multiple_inheritance_cpp
+    struct Base12 : Base1, Base2 {
+        Base12(int i, int j) : Base1(i), Base2(j) { }
+    };
+    struct MIType : Base12 {
+        MIType(int i, int j) : Base12(i, j) { }
+    };
+    py::class_<Base12, Base1, Base2>(m, "Base12");
     py::class_<MIType, Base12>(m, "MIType")
         .def(py::init<int, int>());
 
-    // Many bases for testing that multiple inheritance from many classes (i.e. requiring extra
-    // space for holder constructed flags) works.
+
+    // test_multiple_inheritance_python_many_bases
     #define PYBIND11_BASEN(N) py::class_<BaseN<N>>(m, "BaseN" #N).def(py::init<int>()).def("f" #N, [](BaseN<N> &b) { return b.i + N; })
     PYBIND11_BASEN( 1); PYBIND11_BASEN( 2); PYBIND11_BASEN( 3); PYBIND11_BASEN( 4);
     PYBIND11_BASEN( 5); PYBIND11_BASEN( 6); PYBIND11_BASEN( 7); PYBIND11_BASEN( 8);
@@ -67,55 +94,50 @@ test_initializer multiple_inheritance([](py::module &m) {
 //    };
 //    py::class_<Base12v2>(m, "Base12v2", b1, b2)
 //        .def(py::init<int, int>());
-});
 
-/* Test the case where not all base classes are specified,
-   and where pybind11 requires the py::multiple_inheritance
-   flag to perform proper casting between types */
 
-struct Base1a {
-    Base1a(int i) : i(i) { }
-    int foo() { return i; }
-    int i;
-};
-
-struct Base2a {
-    Base2a(int i) : i(i) { }
-    int bar() { return i; }
-    int i;
-};
-
-struct Base12a : Base1a, Base2a {
-    Base12a(int i, int j) : Base1a(i), Base2a(j) { }
-};
-
-test_initializer multiple_inheritance_nonexplicit([](py::module &m) {
+    // test_multiple_inheritance_virtbase
+    // Test the case where not all base classes are specified, and where pybind11 requires the
+    // py::multiple_inheritance flag to perform proper casting between types.
+    struct Base1a {
+        Base1a(int i) : i(i) { }
+        int foo() { return i; }
+        int i;
+    };
     py::class_<Base1a, std::shared_ptr<Base1a>>(m, "Base1a")
         .def(py::init<int>())
         .def("foo", &Base1a::foo);
 
+    struct Base2a {
+        Base2a(int i) : i(i) { }
+        int bar() { return i; }
+        int i;
+    };
     py::class_<Base2a, std::shared_ptr<Base2a>>(m, "Base2a")
         .def(py::init<int>())
         .def("bar", &Base2a::bar);
 
+    struct Base12a : Base1a, Base2a {
+        Base12a(int i, int j) : Base1a(i), Base2a(j) { }
+    };
     py::class_<Base12a, /* Base1 missing */ Base2a,
                std::shared_ptr<Base12a>>(m, "Base12a", py::multiple_inheritance())
         .def(py::init<int, int>());
 
     m.def("bar_base2a", [](Base2a *b) { return b->bar(); });
     m.def("bar_base2a_sharedptr", [](std::shared_ptr<Base2a> b) { return b->bar(); });
-});
 
-// Issue #801: invalid casting to derived type with MI bases
-struct I801B1 { int a = 1; virtual ~I801B1() = default; };
-struct I801B2 { int b = 2; virtual ~I801B2() = default; };
-struct I801C : I801B1, I801B2 {};
-struct I801D : I801C {}; // Indirect MI
-// Unregistered classes:
-struct I801B3 { int c = 3; virtual ~I801B3() = default; };
-struct I801E : I801B3, I801D {};
+    // test_mi_unaligned_base
+    // test_mi_base_return
+    // Issue #801: invalid casting to derived type with MI bases
+    struct I801B1 { int a = 1; virtual ~I801B1() = default; };
+    struct I801B2 { int b = 2; virtual ~I801B2() = default; };
+    struct I801C : I801B1, I801B2 {};
+    struct I801D : I801C {}; // Indirect MI
+    // Unregistered classes:
+    struct I801B3 { int c = 3; virtual ~I801B3() = default; };
+    struct I801E : I801B3, I801D {};
 
-test_initializer multiple_inheritance_casting([](py::module &m) {
     py::class_<I801B1, std::shared_ptr<I801B1>>(m, "I801B1").def(py::init<>()).def_readonly("a", &I801B1::a);
     py::class_<I801B2, std::shared_ptr<I801B2>>(m, "I801B2").def(py::init<>()).def_readonly("b", &I801B2::b);
     py::class_<I801C, I801B1, I801B2, std::shared_ptr<I801C>>(m, "I801C").def(py::init<>());
@@ -141,46 +163,9 @@ test_initializer multiple_inheritance_casting([](py::module &m) {
     // isn't pybind-registered (and uses multiple-inheritance to offset the pybind base)
     m.def("i801e_c", []() -> I801C * { return new I801E(); });
     m.def("i801e_b2", []() -> I801B2 * { return new I801E(); });
-});
 
 
-struct Vanilla {
-    std::string vanilla() { return "Vanilla"; };
-};
-
-struct WithStatic1 {
-    static std::string static_func1() { return "WithStatic1"; };
-    static int static_value1;
-};
-
-struct WithStatic2 {
-    static std::string static_func2() { return "WithStatic2"; };
-    static int static_value2;
-};
-
-struct WithDict { };
-
-struct VanillaStaticMix1 : Vanilla, WithStatic1, WithStatic2 {
-    static std::string static_func() { return "VanillaStaticMix1"; }
-    static int static_value;
-};
-
-struct VanillaStaticMix2 : WithStatic1, Vanilla, WithStatic2 {
-    static std::string static_func() { return "VanillaStaticMix2"; }
-    static int static_value;
-};
-
-struct VanillaDictMix1 : Vanilla, WithDict { };
-struct VanillaDictMix2 : WithDict, Vanilla { };
-
-int WithStatic1::static_value1 = 1;
-int WithStatic2::static_value2 = 2;
-int VanillaStaticMix1::static_value = 12;
-int VanillaStaticMix2::static_value = 12;
-
-test_initializer mi_static_properties([](py::module &pm) {
-    auto m = pm.def_submodule("mi");
-
+    // test_mi_static_properties
     py::class_<Vanilla>(m, "Vanilla")
         .def(py::init<>())
         .def("vanilla", &Vanilla::vanilla);
@@ -207,9 +192,13 @@ test_initializer mi_static_properties([](py::module &pm) {
         .def_static("static_func", &VanillaStaticMix2::static_func)
         .def_readwrite_static("static_value", &VanillaStaticMix2::static_value);
 
+
 #if !defined(PYPY_VERSION)
+    struct WithDict { };
+    struct VanillaDictMix1 : Vanilla, WithDict { };
+    struct VanillaDictMix2 : WithDict, Vanilla { };
     py::class_<WithDict>(m, "WithDict", py::dynamic_attr()).def(py::init<>());
     py::class_<VanillaDictMix1, Vanilla, WithDict>(m, "VanillaDictMix1").def(py::init<>());
     py::class_<VanillaDictMix2, WithDict, Vanilla>(m, "VanillaDictMix2").def(py::init<>());
 #endif
-});
+}
diff --git a/tests/test_multiple_inheritance.py b/tests/test_multiple_inheritance.py
index 3ed47adcc..7121c81ab 100644
--- a/tests/test_multiple_inheritance.py
+++ b/tests/test_multiple_inheritance.py
@@ -1,19 +1,16 @@
 import pytest
 from pybind11_tests import ConstructorStats
+from pybind11_tests import multiple_inheritance as m
 
 
 def test_multiple_inheritance_cpp():
-    from pybind11_tests import MIType
-
-    mt = MIType(3, 4)
+    mt = m.MIType(3, 4)
 
     assert mt.foo() == 3
     assert mt.bar() == 4
 
 
 def test_multiple_inheritance_mix1():
-    from pybind11_tests import Base2
-
     class Base1:
         def __init__(self, i):
             self.i = i
@@ -21,10 +18,10 @@ def test_multiple_inheritance_mix1():
         def foo(self):
             return self.i
 
-    class MITypePy(Base1, Base2):
+    class MITypePy(Base1, m.Base2):
         def __init__(self, i, j):
             Base1.__init__(self, i)
-            Base2.__init__(self, j)
+            m.Base2.__init__(self, j)
 
     mt = MITypePy(3, 4)
 
@@ -33,7 +30,6 @@ def test_multiple_inheritance_mix1():
 
 
 def test_multiple_inheritance_mix2():
-    from pybind11_tests import Base1
 
     class Base2:
         def __init__(self, i):
@@ -42,9 +38,9 @@ def test_multiple_inheritance_mix2():
         def bar(self):
             return self.i
 
-    class MITypePy(Base1, Base2):
+    class MITypePy(m.Base1, Base2):
         def __init__(self, i, j):
-            Base1.__init__(self, i)
+            m.Base1.__init__(self, i)
             Base2.__init__(self, j)
 
     mt = MITypePy(3, 4)
@@ -54,41 +50,40 @@ def test_multiple_inheritance_mix2():
 
 
 def test_multiple_inheritance_python():
-    from pybind11_tests import Base1, Base2
 
-    class MI1(Base1, Base2):
+    class MI1(m.Base1, m.Base2):
         def __init__(self, i, j):
-            Base1.__init__(self, i)
-            Base2.__init__(self, j)
+            m.Base1.__init__(self, i)
+            m.Base2.__init__(self, j)
 
     class B1(object):
         def v(self):
             return 1
 
-    class MI2(B1, Base1, Base2):
+    class MI2(B1, m.Base1, m.Base2):
         def __init__(self, i, j):
             B1.__init__(self)
-            Base1.__init__(self, i)
-            Base2.__init__(self, j)
+            m.Base1.__init__(self, i)
+            m.Base2.__init__(self, j)
 
     class MI3(MI2):
         def __init__(self, i, j):
             MI2.__init__(self, i, j)
 
-    class MI4(MI3, Base2):
+    class MI4(MI3, m.Base2):
         def __init__(self, i, j, k):
             MI2.__init__(self, j, k)
-            Base2.__init__(self, i)
+            m.Base2.__init__(self, i)
 
-    class MI5(Base2, B1, Base1):
+    class MI5(m.Base2, B1, m.Base1):
         def __init__(self, i, j):
             B1.__init__(self)
-            Base1.__init__(self, i)
-            Base2.__init__(self, j)
+            m.Base1.__init__(self, i)
+            m.Base2.__init__(self, j)
 
-    class MI6(Base2, B1):
+    class MI6(m.Base2, B1):
         def __init__(self, i):
-            Base2.__init__(self, i)
+            m.Base2.__init__(self, i)
             B1.__init__(self)
 
     class B2(B1):
@@ -160,47 +155,45 @@ def test_multiple_inheritance_python():
 
 
 def test_multiple_inheritance_python_many_bases():
-    from pybind11_tests import (BaseN1,  BaseN2,  BaseN3,  BaseN4,  BaseN5,  BaseN6,  BaseN7,
-                                BaseN8,  BaseN9,  BaseN10, BaseN11, BaseN12, BaseN13, BaseN14,
-                                BaseN15, BaseN16, BaseN17)
 
-    class MIMany14(BaseN1, BaseN2, BaseN3, BaseN4):
+    class MIMany14(m.BaseN1, m.BaseN2, m.BaseN3, m.BaseN4):
         def __init__(self):
-            BaseN1.__init__(self, 1)
-            BaseN2.__init__(self, 2)
-            BaseN3.__init__(self, 3)
-            BaseN4.__init__(self, 4)
+            m.BaseN1.__init__(self, 1)
+            m.BaseN2.__init__(self, 2)
+            m.BaseN3.__init__(self, 3)
+            m.BaseN4.__init__(self, 4)
 
-    class MIMany58(BaseN5, BaseN6, BaseN7, BaseN8):
+    class MIMany58(m.BaseN5, m.BaseN6, m.BaseN7, m.BaseN8):
         def __init__(self):
-            BaseN5.__init__(self, 5)
-            BaseN6.__init__(self, 6)
-            BaseN7.__init__(self, 7)
-            BaseN8.__init__(self, 8)
+            m.BaseN5.__init__(self, 5)
+            m.BaseN6.__init__(self, 6)
+            m.BaseN7.__init__(self, 7)
+            m.BaseN8.__init__(self, 8)
 
-    class MIMany916(BaseN9, BaseN10, BaseN11, BaseN12, BaseN13, BaseN14, BaseN15, BaseN16):
+    class MIMany916(m.BaseN9, m.BaseN10, m.BaseN11, m.BaseN12, m.BaseN13, m.BaseN14, m.BaseN15,
+                    m.BaseN16):
         def __init__(self):
-            BaseN9.__init__(self, 9)
-            BaseN10.__init__(self, 10)
-            BaseN11.__init__(self, 11)
-            BaseN12.__init__(self, 12)
-            BaseN13.__init__(self, 13)
-            BaseN14.__init__(self, 14)
-            BaseN15.__init__(self, 15)
-            BaseN16.__init__(self, 16)
+            m.BaseN9.__init__(self, 9)
+            m.BaseN10.__init__(self, 10)
+            m.BaseN11.__init__(self, 11)
+            m.BaseN12.__init__(self, 12)
+            m.BaseN13.__init__(self, 13)
+            m.BaseN14.__init__(self, 14)
+            m.BaseN15.__init__(self, 15)
+            m.BaseN16.__init__(self, 16)
 
-    class MIMany19(MIMany14, MIMany58, BaseN9):
+    class MIMany19(MIMany14, MIMany58, m.BaseN9):
         def __init__(self):
             MIMany14.__init__(self)
             MIMany58.__init__(self)
-            BaseN9.__init__(self, 9)
+            m.BaseN9.__init__(self, 9)
 
-    class MIMany117(MIMany14, MIMany58, MIMany916, BaseN17):
+    class MIMany117(MIMany14, MIMany58, MIMany916, m.BaseN17):
         def __init__(self):
             MIMany14.__init__(self)
             MIMany58.__init__(self)
             MIMany916.__init__(self)
-            BaseN17.__init__(self, 17)
+            m.BaseN17.__init__(self, 17)
 
     # Inherits from 4 registered C++ classes: can fit in one pointer on any modern arch:
     a = MIMany14()
@@ -224,31 +217,29 @@ def test_multiple_inheritance_python_many_bases():
 
 
 def test_multiple_inheritance_virtbase():
-    from pybind11_tests import Base12a, bar_base2a, bar_base2a_sharedptr
 
-    class MITypePy(Base12a):
+    class MITypePy(m.Base12a):
         def __init__(self, i, j):
-            Base12a.__init__(self, i, j)
+            m.Base12a.__init__(self, i, j)
 
     mt = MITypePy(3, 4)
     assert mt.bar() == 4
-    assert bar_base2a(mt) == 4
-    assert bar_base2a_sharedptr(mt) == 4
+    assert m.bar_base2a(mt) == 4
+    assert m.bar_base2a_sharedptr(mt) == 4
 
 
 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"""
-    from pybind11_tests import mi
 
-    for d in (mi.VanillaStaticMix1(), mi.VanillaStaticMix2()):
+    for d in (m.VanillaStaticMix1(), m.VanillaStaticMix2()):
         assert d.vanilla() == "Vanilla"
         assert d.static_func1() == "WithStatic1"
         assert d.static_func2() == "WithStatic2"
         assert d.static_func() == d.__class__.__name__
 
-        mi.WithStatic1.static_value1 = 1
-        mi.WithStatic2.static_value2 = 2
+        m.WithStatic1.static_value1 = 1
+        m.WithStatic2.static_value2 = 2
         assert d.static_value1 == 1
         assert d.static_value2 == 2
         assert d.static_value == 12
@@ -264,30 +255,28 @@ def test_mi_static_properties():
 @pytest.unsupported_on_pypy
 def test_mi_dynamic_attributes():
     """Mixing bases with and without dynamic attribute support"""
-    from pybind11_tests import mi
 
-    for d in (mi.VanillaDictMix1(), mi.VanillaDictMix2()):
+    for d in (m.VanillaDictMix1(), m.VanillaDictMix2()):
         d.dynamic = 1
         assert d.dynamic == 1
 
 
 def test_mi_unaligned_base():
     """Returning an offset (non-first MI) base class pointer should recognize the instance"""
-    from pybind11_tests import I801C, I801D, i801b1_c, i801b2_c, i801b1_d, i801b2_d
 
     n_inst = ConstructorStats.detail_reg_inst()
 
-    c = I801C()
-    d = I801D()
+    c = m.I801C()
+    d = m.I801D()
     # + 4 below because we have the two instances, and each instance has offset base I801B2
     assert ConstructorStats.detail_reg_inst() == n_inst + 4
-    b1c = i801b1_c(c)
+    b1c = m.i801b1_c(c)
     assert b1c is c
-    b2c = i801b2_c(c)
+    b2c = m.i801b2_c(c)
     assert b2c is c
-    b1d = i801b1_d(d)
+    b1d = m.i801b1_d(d)
     assert b1d is d
-    b2d = i801b2_d(d)
+    b2d = m.i801b2_d(d)
     assert b2d is d
 
     assert ConstructorStats.detail_reg_inst() == n_inst + 4  # no extra instances
@@ -299,30 +288,28 @@ def test_mi_unaligned_base():
 
 def test_mi_base_return():
     """Tests returning an offset (non-first MI) base class pointer to a derived instance"""
-    from pybind11_tests import (I801B2, I801C, I801D, i801c_b1, i801c_b2, i801d_b1, i801d_b2,
-                                i801e_c, i801e_b2)
 
     n_inst = ConstructorStats.detail_reg_inst()
 
-    c1 = i801c_b1()
-    assert type(c1) is I801C
+    c1 = m.i801c_b1()
+    assert type(c1) is m.I801C
     assert c1.a == 1
     assert c1.b == 2
 
-    d1 = i801d_b1()
-    assert type(d1) is I801D
+    d1 = m.i801d_b1()
+    assert type(d1) is m.I801D
     assert d1.a == 1
     assert d1.b == 2
 
     assert ConstructorStats.detail_reg_inst() == n_inst + 4
 
-    c2 = i801c_b2()
-    assert type(c2) is I801C
+    c2 = m.i801c_b2()
+    assert type(c2) is m.I801C
     assert c2.a == 1
     assert c2.b == 2
 
-    d2 = i801d_b2()
-    assert type(d2) is I801D
+    d2 = m.i801d_b2()
+    assert type(d2) is m.I801D
     assert d2.a == 1
     assert d2.b == 2
 
@@ -336,11 +323,11 @@ def test_mi_base_return():
     # Returning an unregistered derived type with a registered base; we won't
     # pick up the derived type, obviously, but should still work (as an object
     # of whatever type was returned).
-    e1 = i801e_c()
-    assert type(e1) is I801C
+    e1 = m.i801e_c()
+    assert type(e1) is m.I801C
     assert e1.a == 1
     assert e1.b == 2
 
-    e2 = i801e_b2()
-    assert type(e2) is I801B2
+    e2 = m.i801e_b2()
+    assert type(e2) is m.I801B2
     assert e2.b == 2