Issue #21503: Use test_both() consistently in test_importlib.

Lib/test/test_importlib/builtin/test_finder.py

 from .. import abc
 from .. import util
 
-frozen_machinery, source_machinery = util.import_importlib('importlib.machinery')
+machinery = util.import_importlib('importlib.machinery')
 
 import sys
 import unittest
@@ -44,8 +44,10 @@ class FindSpecTests(abc.FinderTests):
                                                             ['pkg'])
             self.assertIsNone(spec)
 
-Frozen_FindSpecTests, Source_FindSpecTests = util.test_both(FindSpecTests,
-        machinery=[frozen_machinery, source_machinery])
+
+(Frozen_FindSpecTests,
+ Source_FindSpecTests
+ ) = util.test_both(FindSpecTests, machinery=machinery)
 
 
 @unittest.skipIf(util.BUILTINS.good_name is None, 'no reasonable builtin module')
@@ -78,8 +80,10 @@ class FinderTests(abc.FinderTests):
                                                             ['pkg'])
             self.assertIsNone(loader)
 
-Frozen_FinderTests, Source_FinderTests = util.test_both(FinderTests,
-        machinery=[frozen_machinery, source_machinery])
+
+(Frozen_FinderTests,
+ Source_FinderTests
+ ) = util.test_both(FinderTests, machinery=machinery)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/builtin/test_loader.py

 from .. import abc
 from .. import util
 
-frozen_machinery, source_machinery = util.import_importlib('importlib.machinery')
+machinery = util.import_importlib('importlib.machinery')
 
 import sys
 import types
@@ -65,8 +65,9 @@ class LoaderTests(abc.LoaderTests):
         self.assertEqual(cm.exception.name, module_name)
 
 
-Frozen_LoaderTests, Source_LoaderTests = util.test_both(LoaderTests,
-        machinery=[frozen_machinery, source_machinery])
+(Frozen_LoaderTests,
+ Source_LoaderTests
+ ) = util.test_both(LoaderTests, machinery=machinery)
 
 
 @unittest.skipIf(util.BUILTINS.good_name is None, 'no reasonable builtin module')
@@ -98,9 +99,10 @@ class InspectLoaderTests:
             method(util.BUILTINS.bad_name)
         self.assertRaises(util.BUILTINS.bad_name)
 
-Frozen_InspectLoaderTests, Source_InspectLoaderTests = util.test_both(
-        InspectLoaderTests,
-        machinery=[frozen_machinery, source_machinery])
+
+(Frozen_InspectLoaderTests,
+ Source_InspectLoaderTests
+ ) = util.test_both(InspectLoaderTests, machinery=machinery)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/extension/test_case_sensitivity.py

@@ -5,7 +5,7 @@ import unittest
 
 from .. import util
 
-frozen_machinery, source_machinery = util.import_importlib('importlib.machinery')
+machinery = util.import_importlib('importlib.machinery')
 
 
 # XXX find_spec tests
@@ -41,9 +41,10 @@ class ExtensionModuleCaseSensitivityTest:
             loader = self.find_module()
             self.assertTrue(hasattr(loader, 'load_module'))
 
-Frozen_ExtensionCaseSensitivity, Source_ExtensionCaseSensitivity = util.test_both(
-        ExtensionModuleCaseSensitivityTest,
-        machinery=[frozen_machinery, source_machinery])
+
+(Frozen_ExtensionCaseSensitivity,
+ Source_ExtensionCaseSensitivity
+ ) = util.test_both(ExtensionModuleCaseSensitivityTest, machinery=machinery)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/extension/test_finder.py

@@ -35,8 +35,10 @@ class FinderTests(abc.FinderTests):
     def test_failure(self):
         self.assertIsNone(self.find_module('asdfjkl;'))
 
-Frozen_FinderTests, Source_FinderTests = util.test_both(
-        FinderTests, machinery=machinery)
+
+(Frozen_FinderTests,
+ Source_FinderTests
+ ) = util.test_both(FinderTests, machinery=machinery)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/extension/test_loader.py

@@ -76,8 +76,9 @@ class LoaderTests(abc.LoaderTests):
             loader = self.machinery.ExtensionFileLoader('pkg', path)
             self.assertTrue(loader.is_package('pkg'))
 
-Frozen_LoaderTests, Source_LoaderTests = util.test_both(
-        LoaderTests, machinery=machinery)
+(Frozen_LoaderTests,
+ Source_LoaderTests
+ ) = util.test_both(LoaderTests, machinery=machinery)
 
 
 

Lib/test/test_importlib/extension/test_path_hook.py

@@ -23,8 +23,10 @@ class PathHookTests:
         # exists.
         self.assertTrue(hasattr(self.hook(util.EXTENSIONS.path), 'find_module'))
 
-Frozen_PathHooksTests, Source_PathHooksTests = util.test_both(
-        PathHookTests, machinery=machinery)
+
+(Frozen_PathHooksTests,
+ Source_PathHooksTests
+ ) = util.test_both(PathHookTests, machinery=machinery)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/frozen/test_finder.py

@@ -37,8 +37,10 @@ class FindSpecTests(abc.FinderTests):
         spec = self.find('<not real>')
         self.assertIsNone(spec)
 
-Frozen_FindSpecTests, Source_FindSpecTests = util.test_both(FindSpecTests,
-                                                            machinery=machinery)
+
+(Frozen_FindSpecTests,
+ Source_FindSpecTests
+ ) = util.test_both(FindSpecTests, machinery=machinery)
 
 
 class FinderTests(abc.FinderTests):
@@ -72,8 +74,10 @@ class FinderTests(abc.FinderTests):
         loader = self.find('<not real>')
         self.assertIsNone(loader)
 
-Frozen_FinderTests, Source_FinderTests = util.test_both(FinderTests,
-                                                        machinery=machinery)
+
+(Frozen_FinderTests,
+ Source_FinderTests
+ ) = util.test_both(FinderTests, machinery=machinery)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/frozen/test_loader.py

@@ -85,8 +85,10 @@ class ExecModuleTests(abc.LoaderTests):
             self.exec_module('_not_real')
         self.assertEqual(cm.exception.name, '_not_real')
 
-Frozen_ExecModuleTests, Source_ExecModuleTests = util.test_both(ExecModuleTests,
-                                                        machinery=machinery)
+
+(Frozen_ExecModuleTests,
+ Source_ExecModuleTests
+ ) = util.test_both(ExecModuleTests, machinery=machinery)
 
 
 class LoaderTests(abc.LoaderTests):
@@ -175,8 +177,10 @@ class LoaderTests(abc.LoaderTests):
             self.machinery.FrozenImporter.load_module('_not_real')
         self.assertEqual(cm.exception.name, '_not_real')
 
-Frozen_LoaderTests, Source_LoaderTests = util.test_both(LoaderTests,
-                                                        machinery=machinery)
+
+(Frozen_LoaderTests,
+ Source_LoaderTests
+ ) = util.test_both(LoaderTests, machinery=machinery)
 
 
 class InspectLoaderTests:
@@ -214,8 +218,9 @@ class InspectLoaderTests:
                 method('importlib')
             self.assertEqual(cm.exception.name, 'importlib')
 
-Frozen_ILTests, Source_ILTests = util.test_both(InspectLoaderTests,
-                                                machinery=machinery)
+(Frozen_ILTests,
+ Source_ILTests
+ ) = util.test_both(InspectLoaderTests, machinery=machinery)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/import_/test___loader__.py

@@ -23,8 +23,10 @@ class SpecLoaderAttributeTests:
             module = self.__import__('blah')
         self.assertEqual(loader, module.__loader__)
 
-Frozen_SpecTests, Source_SpecTests = util.test_both(
-        SpecLoaderAttributeTests, __import__=util.__import__)
+
+(Frozen_SpecTests,
+ Source_SpecTests
+ ) = util.test_both(SpecLoaderAttributeTests, __import__=util.__import__)
 
 
 class LoaderMock:
@@ -61,8 +63,9 @@ class LoaderAttributeTests:
         self.assertEqual(loader, module.__loader__)
 
 
-Frozen_Tests, Source_Tests = util.test_both(LoaderAttributeTests,
-                                            __import__=util.__import__)
+(Frozen_Tests,
+ Source_Tests
+ ) = util.test_both(LoaderAttributeTests, __import__=util.__import__)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/import_/test___package__.py

@@ -69,17 +69,23 @@ class Using__package__:
         with self.assertRaises(TypeError):
             self.__import__('', globals, {}, ['relimport'], 1)
 
+
 class Using__package__PEP302(Using__package__):
     mock_modules = util.mock_modules
 
-Frozen_UsingPackagePEP302, Source_UsingPackagePEP302 = util.test_both(
-        Using__package__PEP302, __import__=util.__import__)
+
+(Frozen_UsingPackagePEP302,
+ Source_UsingPackagePEP302
+ ) = util.test_both(Using__package__PEP302, __import__=util.__import__)
+
 
 class Using__package__PEP451(Using__package__):
     mock_modules = util.mock_spec
 
-Frozen_UsingPackagePEP451, Source_UsingPackagePEP451 = util.test_both(
-        Using__package__PEP451, __import__=util.__import__)
+
+(Frozen_UsingPackagePEP451,
+ Source_UsingPackagePEP451
+ ) = util.test_both(Using__package__PEP451, __import__=util.__import__)
 
 
 class Setting__package__:
@@ -94,7 +100,7 @@ class Setting__package__:
 
     """
 
-    __import__ = util.__import__[1]
+    __import__ = util.__import__['Source']
 
     # [top-level]
     def test_top_level(self):

Lib/test/test_importlib/import_/test_api.py

@@ -78,15 +78,19 @@ class APITest:
 class OldAPITests(APITest):
     bad_finder_loader = BadLoaderFinder
 
-Frozen_OldAPITests, Source_OldAPITests = util.test_both(
-        OldAPITests, __import__=util.__import__)
+
+(Frozen_OldAPITests,
+ Source_OldAPITests
+ ) = util.test_both(OldAPITests, __import__=util.__import__)
 
 
 class SpecAPITests(APITest):
     bad_finder_loader = BadSpecFinderLoader
 
-Frozen_SpecAPITests, Source_SpecAPITests = util.test_both(
-        SpecAPITests, __import__=util.__import__)
+
+(Frozen_SpecAPITests,
+ Source_SpecAPITests
+ ) = util.test_both(SpecAPITests, __import__=util.__import__)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/import_/test_caching.py

@@ -38,15 +38,17 @@ class UseCache:
                 self.__import__(name)
             self.assertEqual(cm.exception.name, name)
 
-Frozen_UseCache, Source_UseCache = util.test_both(
-        UseCache, __import__=util.__import__)
+
+(Frozen_UseCache,
+ Source_UseCache
+ ) = util.test_both(UseCache, __import__=util.__import__)
 
 
 class ImportlibUseCache(UseCache, unittest.TestCase):
 
     # Pertinent only to PEP 302; exec_module() doesn't return a module.
 
-    __import__ = util.__import__[1]
+    __import__ = util.__import__['Source']
 
     def create_mock(self, *names, return_=None):
         mock = util.mock_modules(*names)

Lib/test/test_importlib/import_/test_fromlist.py

@@ -28,8 +28,10 @@ class ReturnValue:
                 module = self.__import__('pkg.module', fromlist=['attr'])
                 self.assertEqual(module.__name__, 'pkg.module')
 
-Frozen_ReturnValue, Source_ReturnValue = util.test_both(
-        ReturnValue, __import__=util.__import__)
+
+(Frozen_ReturnValue,
+ Source_ReturnValue
+ ) = util.test_both(ReturnValue, __import__=util.__import__)
 
 
 class HandlingFromlist:
@@ -120,8 +122,10 @@ class HandlingFromlist:
                 self.assertEqual(module.module1.__name__, 'pkg.module1')
                 self.assertEqual(module.module2.__name__, 'pkg.module2')
 
-Frozen_FromList, Source_FromList = util.test_both(
-        HandlingFromlist, __import__=util.__import__)
+
+(Frozen_FromList,
+ Source_FromList
+ ) = util.test_both(HandlingFromlist, __import__=util.__import__)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/import_/test_meta_path.py

@@ -45,8 +45,10 @@ class CallingOrder:
                 self.assertEqual(len(w), 1)
                 self.assertTrue(issubclass(w[-1].category, ImportWarning))
 
-Frozen_CallingOrder, Source_CallingOrder = util.test_both(
-        CallingOrder, __import__=util.__import__)
+
+(Frozen_CallingOrder,
+ Source_CallingOrder
+ ) = util.test_both(CallingOrder, __import__=util.__import__)
 
 
 class CallSignature:
@@ -99,19 +101,25 @@ class CallSignature:
                 self.assertEqual(args[0], mod_name)
                 self.assertIs(args[1], path)
 
+
 class CallSignaturePEP302(CallSignature):
     mock_modules = util.mock_modules
     finder_name = 'find_module'
 
-Frozen_CallSignaturePEP302, Source_CallSignaturePEP302 = util.test_both(
-        CallSignaturePEP302, __import__=util.__import__)
+
+(Frozen_CallSignaturePEP302,
+ Source_CallSignaturePEP302
+ ) = util.test_both(CallSignaturePEP302, __import__=util.__import__)
+
 
 class CallSignaturePEP451(CallSignature):
     mock_modules = util.mock_spec
     finder_name = 'find_spec'
 
-Frozen_CallSignaturePEP451, Source_CallSignaturePEP451 = util.test_both(
-        CallSignaturePEP451, __import__=util.__import__)
+
+(Frozen_CallSignaturePEP451,
+ Source_CallSignaturePEP451
+ ) = util.test_both(CallSignaturePEP451, __import__=util.__import__)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/import_/test_packages.py

@@ -101,8 +101,10 @@ class ParentModuleTests:
                 finally:
                     support.unload(subname)
 
-Frozen_ParentTests, Source_ParentTests = util.test_both(
-        ParentModuleTests, __import__=util.__import__)
+
+(Frozen_ParentTests,
+ Source_ParentTests
+ ) = util.test_both(ParentModuleTests, __import__=util.__import__)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/import_/test_path.py

@@ -158,8 +158,10 @@ class FinderTests:
             got = self.machinery.PathFinder.find_spec('whatever', [path])
         self.assertEqual(got, success_finder.spec)
 
-Frozen_FinderTests, Source_FinderTests = util.test_both(
-        FinderTests, importlib=importlib, machinery=machinery)
+
+(Frozen_FinderTests,
+ Source_FinderTests
+ ) = util.test_both(FinderTests, importlib=importlib, machinery=machinery)
 
 
 class PathEntryFinderTests:
@@ -182,8 +184,10 @@ class PathEntryFinderTests:
                                path_hooks=[Finder]):
             self.machinery.PathFinder.find_spec('importlib')
 
-Frozen_PEFTests, Source_PEFTests = util.test_both(
-        PathEntryFinderTests, machinery=machinery)
+
+(Frozen_PEFTests,
+ Source_PEFTests
+ ) = util.test_both(PathEntryFinderTests, machinery=machinery)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/import_/test_relative_imports.py

@@ -207,8 +207,10 @@ class RelativeImports:
         with self.assertRaises(KeyError):
             self.__import__('sys', level=1)
 
-Frozen_RelativeImports, Source_RelativeImports = util.test_both(
-        RelativeImports, __import__=util.__import__)
+
+(Frozen_RelativeImports,
+ Source_RelativeImports
+ ) = util.test_both(RelativeImports, __import__=util.__import__)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/source/test_case_sensitivity.py

@@ -62,20 +62,28 @@ class CaseSensitivityTest:
             self.assertIsNotNone(insensitive)
             self.assertIn(self.name, insensitive.get_filename(self.name))
 
+
 class CaseSensitivityTestPEP302(CaseSensitivityTest):
     def find(self, finder):
         return finder.find_module(self.name)
 
-Frozen_CaseSensitivityTestPEP302, Source_CaseSensitivityTestPEP302 = util.test_both(
-    CaseSensitivityTestPEP302, importlib=importlib, machinery=machinery)
+
+(Frozen_CaseSensitivityTestPEP302,
+ Source_CaseSensitivityTestPEP302
+ ) = util.test_both(CaseSensitivityTestPEP302, importlib=importlib,
+                    machinery=machinery)
+
 
 class CaseSensitivityTestPEP451(CaseSensitivityTest):
     def find(self, finder):
         found = finder.find_spec(self.name)
         return found.loader if found is not None else found
 
-Frozen_CaseSensitivityTestPEP451, Source_CaseSensitivityTestPEP451 = util.test_both(
-    CaseSensitivityTestPEP451, importlib=importlib, machinery=machinery)
+
+(Frozen_CaseSensitivityTestPEP451,
+ Source_CaseSensitivityTestPEP451
+ ) = util.test_both(CaseSensitivityTestPEP451, importlib=importlib,
+                    machinery=machinery)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/source/test_file_loader.py

@@ -235,9 +235,11 @@ class SimpleTest(abc.LoaderTests):
                 warnings.simplefilter('ignore', DeprecationWarning)
                 loader.load_module('bad name')
 
-Frozen_SimpleTest, Source_SimpleTest = util.test_both(
-        SimpleTest, importlib=importlib, machinery=machinery, abc=importlib_abc,
-        util=importlib_util)
+
+(Frozen_SimpleTest,
+ Source_SimpleTest
+ ) = util.test_both(SimpleTest, importlib=importlib, machinery=machinery,
+                    abc=importlib_abc, util=importlib_util)
 
 
 class BadBytecodeTest:
@@ -346,6 +348,7 @@ class BadBytecodeTest:
                                     lambda bc: b'\x00\x00\x00\x00' + bc[4:])
             test('_temp', mapping, bc_path)
 
+
 class BadBytecodeTestPEP451(BadBytecodeTest):
 
     def import_(self, file, module_name):
@@ -354,6 +357,7 @@ class BadBytecodeTestPEP451(BadBytecodeTest):
         module.__spec__ = self.util.spec_from_loader(module_name, loader)
         loader.exec_module(module)
 
+
 class BadBytecodeTestPEP302(BadBytecodeTest):
 
     def import_(self, file, module_name):
@@ -490,21 +494,29 @@ class SourceLoaderBadBytecodeTest:
                 # Make writable for eventual clean-up.
                 os.chmod(bytecode_path, stat.S_IWUSR)
 
+
 class SourceLoaderBadBytecodeTestPEP451(
         SourceLoaderBadBytecodeTest, BadBytecodeTestPEP451):
     pass
 
-Frozen_SourceBadBytecodePEP451, Source_SourceBadBytecodePEP451 = util.test_both(
-        SourceLoaderBadBytecodeTestPEP451, importlib=importlib, machinery=machinery,
-        abc=importlib_abc, util=importlib_util)
+
+(Frozen_SourceBadBytecodePEP451,
+ Source_SourceBadBytecodePEP451
+ ) = util.test_both(SourceLoaderBadBytecodeTestPEP451, importlib=importlib,
+                    machinery=machinery, abc=importlib_abc,
+                    util=importlib_util)
+
 
 class SourceLoaderBadBytecodeTestPEP302(
         SourceLoaderBadBytecodeTest, BadBytecodeTestPEP302):
     pass
 
-Frozen_SourceBadBytecodePEP302, Source_SourceBadBytecodePEP302 = util.test_both(
-        SourceLoaderBadBytecodeTestPEP302, importlib=importlib, machinery=machinery,
-        abc=importlib_abc, util=importlib_util)
+
+(Frozen_SourceBadBytecodePEP302,
+ Source_SourceBadBytecodePEP302
+ ) = util.test_both(SourceLoaderBadBytecodeTestPEP302, importlib=importlib,
+                    machinery=machinery, abc=importlib_abc,
+                    util=importlib_util)
 
 
 class SourcelessLoaderBadBytecodeTest:
@@ -566,21 +578,29 @@ class SourcelessLoaderBadBytecodeTest:
     def test_non_code_marshal(self):
         self._test_non_code_marshal(del_source=True)
 
+
 class SourcelessLoaderBadBytecodeTestPEP451(SourcelessLoaderBadBytecodeTest,
         BadBytecodeTestPEP451):
     pass
 
-Frozen_SourcelessBadBytecodePEP451, Source_SourcelessBadBytecodePEP451 = util.test_both(
-        SourcelessLoaderBadBytecodeTestPEP451, importlib=importlib,
-        machinery=machinery, abc=importlib_abc, util=importlib_util)
+
+(Frozen_SourcelessBadBytecodePEP451,
+ Source_SourcelessBadBytecodePEP451
+ ) = util.test_both(SourcelessLoaderBadBytecodeTestPEP451, importlib=importlib,
+                    machinery=machinery, abc=importlib_abc,
+                    util=importlib_util)
+
 
 class SourcelessLoaderBadBytecodeTestPEP302(SourcelessLoaderBadBytecodeTest,
         BadBytecodeTestPEP302):
     pass
 
-Frozen_SourcelessBadBytecodePEP302, Source_SourcelessBadBytecodePEP302 = util.test_both(
-        SourcelessLoaderBadBytecodeTestPEP302, importlib=importlib,
-        machinery=machinery, abc=importlib_abc, util=importlib_util)
+
+(Frozen_SourcelessBadBytecodePEP302,
+ Source_SourcelessBadBytecodePEP302
+ ) = util.test_both(SourcelessLoaderBadBytecodeTestPEP302, importlib=importlib,
+                    machinery=machinery, abc=importlib_abc,
+                    util=importlib_util)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/source/test_finder.py

@@ -195,8 +195,10 @@ class FinderTestsPEP451(FinderTests):
         spec = finder.find_spec(name)
         return spec.loader if spec is not None else spec
 
-Frozen_FinderTestsPEP451, Source_FinderTestsPEP451 = util.test_both(
-        FinderTestsPEP451, machinery=machinery)
+
+(Frozen_FinderTestsPEP451,
+ Source_FinderTestsPEP451
+ ) = util.test_both(FinderTestsPEP451, machinery=machinery)
 
 
 class FinderTestsPEP420(FinderTests):
@@ -209,8 +211,10 @@ class FinderTestsPEP420(FinderTests):
             loader_portions = finder.find_loader(name)
             return loader_portions[0] if loader_only else loader_portions
 
-Frozen_FinderTestsPEP420, Source_FinderTestsPEP420 = util.test_both(
-        FinderTestsPEP420, machinery=machinery)
+
+(Frozen_FinderTestsPEP420,
+ Source_FinderTestsPEP420
+ ) = util.test_both(FinderTestsPEP420, machinery=machinery)
 
 
 class FinderTestsPEP302(FinderTests):
@@ -222,9 +226,10 @@ class FinderTestsPEP302(FinderTests):
             warnings.simplefilter("ignore", DeprecationWarning)
             return finder.find_module(name)
 
-Frozen_FinderTestsPEP302, Source_FinderTestsPEP302 = util.test_both(
-        FinderTestsPEP302, machinery=machinery)
 
+(Frozen_FinderTestsPEP302,
+ Source_FinderTestsPEP302
+ ) = util.test_both(FinderTestsPEP302, machinery=machinery)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/source/test_path_hook.py

@@ -22,7 +22,10 @@ class PathHookTest:
         # The empty string represents the cwd.
         self.assertTrue(hasattr(self.path_hook()(''), 'find_module'))
 
-Frozen_PathHookTest, Source_PathHooktest = util.test_both(PathHookTest, machinery=machinery)
+
+(Frozen_PathHookTest,
+ Source_PathHooktest
+ ) = util.test_both(PathHookTest, machinery=machinery)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/source/test_source_encoding.py

@@ -88,6 +88,7 @@ class EncodingTest:
         with self.assertRaises(SyntaxError):
             self.run_test(source)
 
+
 class EncodingTestPEP451(EncodingTest):
 
     def load(self, loader):
@@ -96,8 +97,11 @@ class EncodingTestPEP451(EncodingTest):
         loader.exec_module(module)
         return module
 
-Frozen_EncodingTestPEP451, Source_EncodingTestPEP451 = util.test_both(
-        EncodingTestPEP451, machinery=machinery)
+
+(Frozen_EncodingTestPEP451,
+ Source_EncodingTestPEP451
+ ) = util.test_both(EncodingTestPEP451, machinery=machinery)
+
 
 class EncodingTestPEP302(EncodingTest):
 
@@ -106,8 +110,10 @@ class EncodingTestPEP302(EncodingTest):
             warnings.simplefilter('ignore', DeprecationWarning)
             return loader.load_module(self.module_name)
 
-Frozen_EncodingTestPEP302, Source_EncodingTestPEP302 = util.test_both(
-        EncodingTestPEP302, machinery=machinery)
+
+(Frozen_EncodingTestPEP302,
+ Source_EncodingTestPEP302
+ ) = util.test_both(EncodingTestPEP302, machinery=machinery)
 
 
 class LineEndingTest:
@@ -138,6 +144,7 @@ class LineEndingTest:
     def test_lf(self):
         self.run_test(b'\n')
 
+
 class LineEndingTestPEP451(LineEndingTest):
 
     def load(self, loader, module_name):
@@ -146,8 +153,11 @@ class LineEndingTestPEP451(LineEndingTest):
         loader.exec_module(module)
         return module
 
-Frozen_LineEndingTestPEP451, Source_LineEndingTestPEP451 = util.test_both(
-        LineEndingTestPEP451, machinery=machinery)
+
+(Frozen_LineEndingTestPEP451,
+ Source_LineEndingTestPEP451
+ ) = util.test_both(LineEndingTestPEP451, machinery=machinery)
+
 
 class LineEndingTestPEP302(LineEndingTest):
 
@@ -156,8 +166,10 @@ class LineEndingTestPEP302(LineEndingTest):
             warnings.simplefilter('ignore', DeprecationWarning)
             return loader.load_module(module_name)
 
-Frozen_LineEndingTestPEP302, Source_LineEndingTestPEP302 = util.test_both(
-        LineEndingTestPEP302, machinery=machinery)
+
+(Frozen_LineEndingTestPEP302,
+ Source_LineEndingTestPEP302
+ ) = util.test_both(LineEndingTestPEP302, machinery=machinery)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/test_abc.py

@@ -10,12 +10,13 @@ import unittest
 from unittest import mock
 import warnings
 
-from . import util
+from . import util as test_util
+
+init = test_util.import_importlib('importlib')
+abc = test_util.import_importlib('importlib.abc')
+machinery = test_util.import_importlib('importlib.machinery')
+util = test_util.import_importlib('importlib.util')
 
-frozen_init, source_init = util.import_importlib('importlib')
-frozen_abc, source_abc = util.import_importlib('importlib.abc')
-machinery = util.import_importlib('importlib.machinery')
-frozen_util, source_util = util.import_importlib('importlib.util')
 
 ##### Inheritance ##############################################################
 class InheritanceTests:
@@ -26,8 +27,7 @@ class InheritanceTests:
     subclasses = []
     superclasses = []
 
-    def __init__(self, *args, **kwargs):
-        super().__init__(*args, **kwargs)
+    def setUp(self):
         self.superclasses = [getattr(self.abc, class_name)
                              for class_name in self.superclass_names]
         if hasattr(self, 'subclass_names'):
@@ -36,11 +36,11 @@ class InheritanceTests:
             # checking across module boundaries (i.e. the _bootstrap in abc is
             # not the same as the one in machinery). That means stealing one of
             # the modules from the other to make sure the same instance is used.
-            self.subclasses = [getattr(self.abc.machinery, class_name)
+            machinery = self.abc.machinery
+            self.subclasses = [getattr(machinery, class_name)
                                for class_name in self.subclass_names]
         assert self.subclasses or self.superclasses, self.__class__
-        testing = self.__class__.__name__.partition('_')[2]
-        self.__test = getattr(self.abc, testing)
+        self.__test = getattr(self.abc, self._NAME)
 
     def test_subclasses(self):
         # Test that the expected subclasses inherit.
@@ -54,94 +54,97 @@ class InheritanceTests:
             self.assertTrue(issubclass(self.__test, superclass),
                "{0} is not a superclass of {1}".format(superclass, self.__test))
 
-def create_inheritance_tests(base_class):
-    def set_frozen(ns):
-        ns['abc'] = frozen_abc
-    def set_source(ns):
-        ns['abc'] = source_abc
-
-    classes = []
-    for prefix, ns_set in [('Frozen', set_frozen), ('Source', set_source)]:
-        classes.append(types.new_class('_'.join([prefix, base_class.__name__]),
-                                       (base_class, unittest.TestCase),
-                                       exec_body=ns_set))
-    return classes
-
 
 class MetaPathFinder(InheritanceTests):
     superclass_names = ['Finder']
     subclass_names = ['BuiltinImporter', 'FrozenImporter', 'PathFinder',
                       'WindowsRegistryFinder']
 
-tests = create_inheritance_tests(MetaPathFinder)
-Frozen_MetaPathFinderInheritanceTests, Source_MetaPathFinderInheritanceTests = tests
+
+(Frozen_MetaPathFinderInheritanceTests,
+ Source_MetaPathFinderInheritanceTests
+ ) = test_util.test_both(MetaPathFinder, abc=abc)
 
 
 class PathEntryFinder(InheritanceTests):
     superclass_names = ['Finder']
     subclass_names = ['FileFinder']
 
-tests = create_inheritance_tests(PathEntryFinder)
-Frozen_PathEntryFinderInheritanceTests, Source_PathEntryFinderInheritanceTests = tests
+
+(Frozen_PathEntryFinderInheritanceTests,
+ Source_PathEntryFinderInheritanceTests
+ ) = test_util.test_both(PathEntryFinder, abc=abc)
 
 
 class ResourceLoader(InheritanceTests):
     superclass_names = ['Loader']
 
-tests = create_inheritance_tests(ResourceLoader)
-Frozen_ResourceLoaderInheritanceTests, Source_ResourceLoaderInheritanceTests = tests
+
+(Frozen_ResourceLoaderInheritanceTests,
+ Source_ResourceLoaderInheritanceTests
+ ) = test_util.test_both(ResourceLoader, abc=abc)
 
 
 class InspectLoader(InheritanceTests):
     superclass_names = ['Loader']
     subclass_names = ['BuiltinImporter', 'FrozenImporter', 'ExtensionFileLoader']
 
-tests = create_inheritance_tests(InspectLoader)
-Frozen_InspectLoaderInheritanceTests, Source_InspectLoaderInheritanceTests = tests
+
+(Frozen_InspectLoaderInheritanceTests,
+ Source_InspectLoaderInheritanceTests
+ ) = test_util.test_both(InspectLoader, abc=abc)
 
 
 class ExecutionLoader(InheritanceTests):
     superclass_names = ['InspectLoader']
     subclass_names = ['ExtensionFileLoader']
 
-tests = create_inheritance_tests(ExecutionLoader)
-Frozen_ExecutionLoaderInheritanceTests, Source_ExecutionLoaderInheritanceTests = tests
+
+(Frozen_ExecutionLoaderInheritanceTests,
+ Source_ExecutionLoaderInheritanceTests
+ ) = test_util.test_both(ExecutionLoader, abc=abc)
 
 
 class FileLoader(InheritanceTests):
     superclass_names = ['ResourceLoader', 'ExecutionLoader']
     subclass_names = ['SourceFileLoader', 'SourcelessFileLoader']
 
-tests = create_inheritance_tests(FileLoader)
-Frozen_FileLoaderInheritanceTests, Source_FileLoaderInheritanceTests = tests
+
+(Frozen_FileLoaderInheritanceTests,
+ Source_FileLoaderInheritanceTests
+ ) = test_util.test_both(FileLoader, abc=abc)
 
 
 class SourceLoader(InheritanceTests):
     superclass_names = ['ResourceLoader', 'ExecutionLoader']
     subclass_names = ['SourceFileLoader']
 
-tests = create_inheritance_tests(SourceLoader)
-Frozen_SourceLoaderInheritanceTests, Source_SourceLoaderInheritanceTests = tests
+
+(Frozen_SourceLoaderInheritanceTests,
+ Source_SourceLoaderInheritanceTests
+ ) = test_util.test_both(SourceLoader, abc=abc)
+
 
 ##### Default return values ####################################################
-def make_abc_subclasses(base_class):
-    classes = []
-    for kind, abc in [('Frozen', frozen_abc), ('Source', source_abc)]:
-        name = '_'.join([kind, base_class.__name__])
-        base_classes = base_class, getattr(abc, base_class.__name__)
-        classes.append(types.new_class(name, base_classes))
-    return classes
-
-def make_return_value_tests(base_class, test_class):
-    frozen_class, source_class = make_abc_subclasses(base_class)
-    tests = []
-    for prefix, class_in_test in [('Frozen', frozen_class), ('Source', source_class)]:
-        def set_ns(ns):
-            ns['ins'] = class_in_test()
-        tests.append(types.new_class('_'.join([prefix, test_class.__name__]),
-                                     (test_class, unittest.TestCase),
-                                     exec_body=set_ns))
-    return tests
+
+def make_abc_subclasses(base_class, name=None, inst=False, **kwargs):
+    if name is None:
+        name = base_class.__name__
+    base = {kind: getattr(splitabc, name)
+            for kind, splitabc in abc.items()}
+    return {cls._KIND: cls() if inst else cls
+            for cls in test_util.split_frozen(base_class, base, **kwargs)}
+
+
+class ABCTestHarness:
+
+    @property
+    def ins(self):
+        # Lazily set ins on the class.
+        cls = self.SPLIT[self._KIND]
+        ins = cls()
+        self.__class__.ins = ins
+        return ins
 
 
 class MetaPathFinder:
@@ -149,10 +152,10 @@ class MetaPathFinder:
     def find_module(self, fullname, path):
         return super().find_module(fullname, path)
 
-Frozen_MPF, Source_MPF = make_abc_subclasses(MetaPathFinder)
 
+class MetaPathFinderDefaultsTests(ABCTestHarness):
 
-class MetaPathFinderDefaultsTests:
+    SPLIT = make_abc_subclasses(MetaPathFinder)
 
     def test_find_module(self):
         # Default should return None.
@@ -163,8 +166,9 @@ class MetaPathFinderDefaultsTests:
         self.ins.invalidate_caches()
 
 
-tests = make_return_value_tests(MetaPathFinder, MetaPathFinderDefaultsTests)
-Frozen_MPFDefaultTests, Source_MPFDefaultTests = tests
+(Frozen_MPFDefaultTests,
+ Source_MPFDefaultTests
+ ) = test_util.test_both(MetaPathFinderDefaultsTests)
 
 
 class PathEntryFinder:
@@ -172,10 +176,10 @@ class PathEntryFinder:
     def find_loader(self, fullname):
         return super().find_loader(fullname)
 
-Frozen_PEF, Source_PEF = make_abc_subclasses(PathEntryFinder)
 
+class PathEntryFinderDefaultsTests(ABCTestHarness):
 
-class PathEntryFinderDefaultsTests:
+    SPLIT = make_abc_subclasses(PathEntryFinder)
 
     def test_find_loader(self):
         self.assertEqual((None, []), self.ins.find_loader('something'))
@@ -188,8 +192,9 @@ class PathEntryFinderDefaultsTests:
         self.ins.invalidate_caches()
 
 
-tests = make_return_value_tests(PathEntryFinder, PathEntryFinderDefaultsTests)
-Frozen_PEFDefaultTests, Source_PEFDefaultTests = tests
+(Frozen_PEFDefaultTests,
+ Source_PEFDefaultTests
+ ) = test_util.test_both(PathEntryFinderDefaultsTests)
 
 
 class Loader:
@@ -198,10 +203,9 @@ class Loader:
         return super().load_module(fullname)
 
 
-Frozen_L, Source_L = make_abc_subclasses(Loader)
+class LoaderDefaultsTests(ABCTestHarness):
 
-
-class LoaderDefaultsTests:
+    SPLIT = make_abc_subclasses(Loader)
 
     def test_load_module(self):
         with self.assertRaises(ImportError):
@@ -217,8 +221,9 @@ class LoaderDefaultsTests:
         self.assertTrue(repr(mod))
 
 
-tests = make_return_value_tests(Loader, LoaderDefaultsTests)
-Frozen_LDefaultTests, SourceLDefaultTests = tests
+(Frozen_LDefaultTests,
+ SourceLDefaultTests
+ ) = test_util.test_both(LoaderDefaultsTests)
 
 
 class ResourceLoader(Loader):
@@ -227,18 +232,18 @@ class ResourceLoader(Loader):
         return super().get_data(path)
 
 
-Frozen_RL, Source_RL = make_abc_subclasses(ResourceLoader)
-
+class ResourceLoaderDefaultsTests(ABCTestHarness):
 
-class ResourceLoaderDefaultsTests:
+    SPLIT = make_abc_subclasses(ResourceLoader)
 
     def test_get_data(self):
         with self.assertRaises(IOError):
             self.ins.get_data('/some/path')
 
 
-tests = make_return_value_tests(ResourceLoader, ResourceLoaderDefaultsTests)
-Frozen_RLDefaultTests, Source_RLDefaultTests = tests
+(Frozen_RLDefaultTests,
+ Source_RLDefaultTests
+ ) = test_util.test_both(ResourceLoaderDefaultsTests)
 
 
 class InspectLoader(Loader):
@@ -250,10 +255,12 @@ class InspectLoader(Loader):
         return super().get_source(fullname)
 
 
-Frozen_IL, Source_IL = make_abc_subclasses(InspectLoader)
+SPLIT_IL = make_abc_subclasses(InspectLoader)
 
 
-class InspectLoaderDefaultsTests:
+class InspectLoaderDefaultsTests(ABCTestHarness):
+
+    SPLIT = SPLIT_IL
 
     def test_is_package(self):
         with self.assertRaises(ImportError):
@@ -264,8 +271,9 @@ class InspectLoaderDefaultsTests:
             self.ins.get_source('blah')
 
 
-tests = make_return_value_tests(InspectLoader, InspectLoaderDefaultsTests)
-Frozen_ILDefaultTests, Source_ILDefaultTests = tests
+(Frozen_ILDefaultTests,
+ Source_ILDefaultTests
+ ) = test_util.test_both(InspectLoaderDefaultsTests)
 
 
 class ExecutionLoader(InspectLoader):
@@ -273,21 +281,25 @@ class ExecutionLoader(InspectLoader):
     def get_filename(self, fullname):
         return super().get_filename(fullname)
 
-Frozen_EL, Source_EL = make_abc_subclasses(ExecutionLoader)
+
+SPLIT_EL = make_abc_subclasses(ExecutionLoader)
 
 
-class ExecutionLoaderDefaultsTests:
+class ExecutionLoaderDefaultsTests(ABCTestHarness):
+
+    SPLIT = SPLIT_EL
 
     def test_get_filename(self):
         with self.assertRaises(ImportError):
             self.ins.get_filename('blah')
 
 
-tests = make_return_value_tests(ExecutionLoader, InspectLoaderDefaultsTests)
-Frozen_ELDefaultTests, Source_ELDefaultsTests = tests
+(Frozen_ELDefaultTests,
+ Source_ELDefaultsTests
+ ) = test_util.test_both(InspectLoaderDefaultsTests)
 
-##### MetaPathFinder concrete methods ##########################################
 
+##### MetaPathFinder concrete methods ##########################################
 class MetaPathFinderFindModuleTests:
 
     @classmethod
@@ -317,13 +329,12 @@ class MetaPathFinderFindModuleTests:
         self.assertIs(found, spec.loader)
 
 
-Frozen_MPFFindModuleTests, Source_MPFFindModuleTests = util.test_both(
-        MetaPathFinderFindModuleTests,
-        abc=(frozen_abc, source_abc),
-        util=(frozen_util, source_util))
+(Frozen_MPFFindModuleTests,
+ Source_MPFFindModuleTests
+ ) = test_util.test_both(MetaPathFinderFindModuleTests, abc=abc, util=util)
 
-##### PathEntryFinder concrete methods #########################################
 
+##### PathEntryFinder concrete methods #########################################
 class PathEntryFinderFindLoaderTests:
 
     @classmethod
@@ -361,11 +372,10 @@ class PathEntryFinderFindLoaderTests:
         self.assertEqual(paths, found[1])
 
 
-Frozen_PEFFindLoaderTests, Source_PEFFindLoaderTests = util.test_both(
-        PathEntryFinderFindLoaderTests,
-        abc=(frozen_abc, source_abc),
-        machinery=machinery,
-        util=(frozen_util, source_util))
+(Frozen_PEFFindLoaderTests,
+ Source_PEFFindLoaderTests
+ ) = test_util.test_both(PathEntryFinderFindLoaderTests, abc=abc, util=util,
+                         machinery=machinery)
 
 
 ##### Loader concrete methods ##################################################
@@ -386,7 +396,7 @@ class LoaderLoadModuleTests:
     def test_fresh(self):
         loader = self.loader()
         name = 'blah'
-        with util.uncache(name):
+        with test_util.uncache(name):
             loader.load_module(name)
             module = loader.found
             self.assertIs(sys.modules[name], module)
@@ -404,7 +414,7 @@ class LoaderLoadModuleTests:
         module = types.ModuleType(name)
         module.__spec__ = self.util.spec_from_loader(name, loader)
         module.__loader__ = loader
-        with util.uncache(name):
+        with test_util.uncache(name):
             sys.modules[name] = module
             loader.load_module(name)
             found = loader.found
@@ -412,10 +422,9 @@ class LoaderLoadModuleTests:
             self.assertIs(module, sys.modules[name])
 
 
-Frozen_LoaderLoadModuleTests, Source_LoaderLoadModuleTests = util.test_both(
-        LoaderLoadModuleTests,
-        abc=(frozen_abc, source_abc),
-        util=(frozen_util, source_util))
+(Frozen_LoaderLoadModuleTests,
+ Source_LoaderLoadModuleTests
+ ) = test_util.test_both(LoaderLoadModuleTests, abc=abc, util=util)
 
 
 ##### InspectLoader concrete methods ###########################################
@@ -461,11 +470,10 @@ class InspectLoaderSourceToCodeTests:
         self.assertEqual(code.co_filename, '<string>')
 
 
-class Frozen_ILSourceToCodeTests(InspectLoaderSourceToCodeTests, unittest.TestCase):
-    InspectLoaderSubclass = Frozen_IL
-
-class Source_ILSourceToCodeTests(InspectLoaderSourceToCodeTests, unittest.TestCase):
-    InspectLoaderSubclass = Source_IL
+(Frozen_ILSourceToCodeTests,
+ Source_ILSourceToCodeTests
+ ) = test_util.test_both(InspectLoaderSourceToCodeTests,
+                         InspectLoaderSubclass=SPLIT_IL)
 
 
 class InspectLoaderGetCodeTests:
@@ -495,11 +503,10 @@ class InspectLoaderGetCodeTests:
             loader.get_code('blah')
 
 
-class Frozen_ILGetCodeTests(InspectLoaderGetCodeTests, unittest.TestCase):
-    InspectLoaderSubclass = Frozen_IL
-
-class Source_ILGetCodeTests(InspectLoaderGetCodeTests, unittest.TestCase):
-    InspectLoaderSubclass = Source_IL
+(Frozen_ILGetCodeTests,
+ Source_ILGetCodeTests
+ ) = test_util.test_both(InspectLoaderGetCodeTests,
+                         InspectLoaderSubclass=SPLIT_IL)
 
 
 class InspectLoaderLoadModuleTests:
@@ -543,11 +550,10 @@ class InspectLoaderLoadModuleTests:
             self.assertEqual(module, sys.modules[self.module_name])
 
 
-class Frozen_ILLoadModuleTests(InspectLoaderLoadModuleTests, unittest.TestCase):
-    InspectLoaderSubclass = Frozen_IL
-
-class Source_ILLoadModuleTests(InspectLoaderLoadModuleTests, unittest.TestCase):
-    InspectLoaderSubclass = Source_IL
+(Frozen_ILLoadModuleTests,
+ Source_ILLoadModuleTests
+ ) = test_util.test_both(InspectLoaderLoadModuleTests,
+                         InspectLoaderSubclass=SPLIT_IL)
 
 
 ##### ExecutionLoader concrete methods #########################################
@@ -608,15 +614,14 @@ class ExecutionLoaderGetCodeTests:
         self.assertEqual(module.attr, 42)
 
 
-class Frozen_ELGetCodeTests(ExecutionLoaderGetCodeTests, unittest.TestCase):
-    ExecutionLoaderSubclass = Frozen_EL
-
-class Source_ELGetCodeTests(ExecutionLoaderGetCodeTests, unittest.TestCase):
-    ExecutionLoaderSubclass = Source_EL
+(Frozen_ELGetCodeTests,
+ Source_ELGetCodeTests
+ ) = test_util.test_both(ExecutionLoaderGetCodeTests,
+                         ExecutionLoaderSubclass=SPLIT_EL)
 
 
 ##### SourceLoader concrete methods ############################################
-class SourceLoader:
+class SourceOnlyLoader:
 
     # Globals that should be defined for all modules.
     source = (b"_ = '::'.join([__name__, __file__, __cached__, __package__, "
@@ -637,10 +642,10 @@ class SourceLoader:
         return '<module>'
 
 
-Frozen_SourceOnlyL, Source_SourceOnlyL = make_abc_subclasses(SourceLoader)
+SPLIT_SOL = make_abc_subclasses(SourceOnlyLoader, 'SourceLoader')
 
 
-class SourceLoader(SourceLoader):
+class SourceLoader(SourceOnlyLoader):
 
     source_mtime = 1
 
@@ -677,11 +682,7 @@ class SourceLoader(SourceLoader):
         return path == self.bytecode_path
 
 
-Frozen_SL, Source_SL = make_abc_subclasses(SourceLoader)
-Frozen_SL.util = frozen_util
-Source_SL.util = source_util
-Frozen_SL.init = frozen_init
-Source_SL.init = source_init
+SPLIT_SL = make_abc_subclasses(SourceLoader, util=util, init=init)
 
 
 class SourceLoaderTestHarness:
@@ -765,7 +766,7 @@ class SourceOnlyLoaderTests(SourceLoaderTestHarness):
         # Loading a module should set __name__, __loader__, __package__,
         # __path__ (for packages), __file__, and __cached__.
         # The module should also be put into sys.modules.
-        with util.uncache(self.name):
+        with test_util.uncache(self.name):
             with warnings.catch_warnings():
                 warnings.simplefilter('ignore', DeprecationWarning)
                 module = self.loader.load_module(self.name)
@@ -778,7 +779,7 @@ class SourceOnlyLoaderTests(SourceLoaderTestHarness):
         # is a package.
         # Testing the values for a package are covered by test_load_module.
         self.setUp(is_package=False)
-        with util.uncache(self.name):
+        with test_util.uncache(self.name):
             with warnings.catch_warnings():
                 warnings.simplefilter('ignore', DeprecationWarning)
                 module = self.loader.load_module(self.name)
@@ -798,13 +799,10 @@ class SourceOnlyLoaderTests(SourceLoaderTestHarness):
         self.assertEqual(returned_source, source)
 
 
-class Frozen_SourceOnlyLTests(SourceOnlyLoaderTests, unittest.TestCase):
-    loader_mock = Frozen_SourceOnlyL
-    util = frozen_util
-
-class Source_SourceOnlyLTests(SourceOnlyLoaderTests, unittest.TestCase):
-    loader_mock = Source_SourceOnlyL
-    util = source_util
+(Frozen_SourceOnlyLoaderTests,
+ Source_SourceOnlyLoaderTests
+ ) = test_util.test_both(SourceOnlyLoaderTests, util=util,
+                         loader_mock=SPLIT_SOL)
 
 
 @unittest.skipIf(sys.dont_write_bytecode, "sys.dont_write_bytecode is true")
@@ -896,15 +894,10 @@ class SourceLoaderBytecodeTests(SourceLoaderTestHarness):
         self.verify_code(code_object)
 
 
-class Frozen_SLBytecodeTests(SourceLoaderBytecodeTests, unittest.TestCase):
-    loader_mock = Frozen_SL
-    init = frozen_init
-    util = frozen_util
-
-class SourceSLBytecodeTests(SourceLoaderBytecodeTests, unittest.TestCase):
-    loader_mock = Source_SL
-    init = source_init
-    util = source_util
+(Frozen_SLBytecodeTests,
+ SourceSLBytecodeTests
+ ) = test_util.test_both(SourceLoaderBytecodeTests, init=init, util=util,
+                         loader_mock=SPLIT_SL)
 
 
 class SourceLoaderGetSourceTests:
@@ -940,11 +933,10 @@ class SourceLoaderGetSourceTests:
         self.assertEqual(mock.get_source(name), expect)
 
 
-class Frozen_SourceOnlyLGetSourceTests(SourceLoaderGetSourceTests, unittest.TestCase):
-    SourceOnlyLoaderMock = Frozen_SourceOnlyL
-
-class Source_SourceOnlyLGetSourceTests(SourceLoaderGetSourceTests, unittest.TestCase):
-    SourceOnlyLoaderMock = Source_SourceOnlyL
+(Frozen_SourceOnlyLoaderGetSourceTests,
+ Source_SourceOnlyLoaderGetSourceTests
+ ) = test_util.test_both(SourceLoaderGetSourceTests,
+                         SourceOnlyLoaderMock=SPLIT_SOL)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/test_api.py

-from . import util
+from . import util as test_util
 
-frozen_init, source_init = util.import_importlib('importlib')
-frozen_util, source_util = util.import_importlib('importlib.util')
-frozen_machinery, source_machinery = util.import_importlib('importlib.machinery')
+init = test_util.import_importlib('importlib')
+util = test_util.import_importlib('importlib.util')
+machinery = test_util.import_importlib('importlib.machinery')
 
 import os.path
 import sys
@@ -18,8 +18,8 @@ class ImportModuleTests:
 
     def test_module_import(self):
         # Test importing a top-level module.
-        with util.mock_modules('top_level') as mock:
-            with util.import_state(meta_path=[mock]):
+        with test_util.mock_modules('top_level') as mock:
+            with test_util.import_state(meta_path=[mock]):
                 module = self.init.import_module('top_level')
                 self.assertEqual(module.__name__, 'top_level')
 
@@ -28,8 +28,8 @@ class ImportModuleTests:
         pkg_name = 'pkg'
         pkg_long_name = '{0}.__init__'.format(pkg_name)
         name = '{0}.mod'.format(pkg_name)
-        with util.mock_modules(pkg_long_name, name) as mock:
-            with util.import_state(meta_path=[mock]):
+        with test_util.mock_modules(pkg_long_name, name) as mock:
+            with test_util.import_state(meta_path=[mock]):
                 module = self.init.import_module(name)
                 self.assertEqual(module.__name__, name)
 
@@ -40,16 +40,16 @@ class ImportModuleTests:
         module_name = 'mod'
         absolute_name = '{0}.{1}'.format(pkg_name, module_name)
         relative_name = '.{0}'.format(module_name)
-        with util.mock_modules(pkg_long_name, absolute_name) as mock:
-            with util.import_state(meta_path=[mock]):
+        with test_util.mock_modules(pkg_long_name, absolute_name) as mock:
+            with test_util.import_state(meta_path=[mock]):
                 self.init.import_module(pkg_name)
                 module = self.init.import_module(relative_name, pkg_name)
                 self.assertEqual(module.__name__, absolute_name)
 
     def test_deep_relative_package_import(self):
         modules = ['a.__init__', 'a.b.__init__', 'a.c']
-        with util.mock_modules(*modules) as mock:
-            with util.import_state(meta_path=[mock]):
+        with test_util.mock_modules(*modules) as mock:
+            with test_util.import_state(meta_path=[mock]):
                 self.init.import_module('a')
                 self.init.import_module('a.b')
                 module = self.init.import_module('..c', 'a.b')
@@ -61,8 +61,8 @@ class ImportModuleTests:
         pkg_name = 'pkg'
         pkg_long_name = '{0}.__init__'.format(pkg_name)
         name = '{0}.mod'.format(pkg_name)
-        with util.mock_modules(pkg_long_name, name) as mock:
-            with util.import_state(meta_path=[mock]):
+        with test_util.mock_modules(pkg_long_name, name) as mock:
+            with test_util.import_state(meta_path=[mock]):
                 self.init.import_module(pkg_name)
                 module = self.init.import_module(name, pkg_name)
                 self.assertEqual(module.__name__, name)
@@ -86,16 +86,15 @@ class ImportModuleTests:
             b_load_count += 1
         code = {'a': load_a, 'a.b': load_b}
         modules = ['a.__init__', 'a.b']
-        with util.mock_modules(*modules, module_code=code) as mock:
-            with util.import_state(meta_path=[mock]):
+        with test_util.mock_modules(*modules, module_code=code) as mock:
+            with test_util.import_state(meta_path=[mock]):
                 self.init.import_module('a.b')
         self.assertEqual(b_load_count, 1)
 
-class Frozen_ImportModuleTests(ImportModuleTests, unittest.TestCase):
-    init = frozen_init
 
-class Source_ImportModuleTests(ImportModuleTests, unittest.TestCase):
-    init = source_init
+(Frozen_ImportModuleTests,
+ Source_ImportModuleTests
+ ) = test_util.test_both(ImportModuleTests, init=init)
 
 
 class FindLoaderTests:
@@ -107,7 +106,7 @@ class FindLoaderTests:
     def test_sys_modules(self):
         # If a module with __loader__ is in sys.modules, then return it.
         name = 'some_mod'
-        with util.uncache(name):
+        with test_util.uncache(name):
             module = types.ModuleType(name)
             loader = 'a loader!'
             module.__loader__ = loader
@@ -120,7 +119,7 @@ class FindLoaderTests:
     def test_sys_modules_loader_is_None(self):
         # If sys.modules[name].__loader__ is None, raise ValueError.
         name = 'some_mod'
-        with util.uncache(name):
+        with test_util.uncache(name):
             module = types.ModuleType(name)
             module.__loader__ = None
             sys.modules[name] = module
@@ -133,7 +132,7 @@ class FindLoaderTests:
         # Should raise ValueError
         # Issue #17099
         name = 'some_mod'
-        with util.uncache(name):
+        with test_util.uncache(name):
             module = types.ModuleType(name)
             try:
                 del module.__loader__
@@ -148,8 +147,8 @@ class FindLoaderTests:
     def test_success(self):
         # Return the loader found on sys.meta_path.
         name = 'some_mod'
-        with util.uncache(name):
-            with util.import_state(meta_path=[self.FakeMetaFinder]):
+        with test_util.uncache(name):
+            with test_util.import_state(meta_path=[self.FakeMetaFinder]):
                 with warnings.catch_warnings():
                     warnings.simplefilter('ignore', DeprecationWarning)
                     self.assertEqual((name, None), self.init.find_loader(name))
@@ -158,8 +157,8 @@ class FindLoaderTests:
         # Searching on a path should work.
         name = 'some_mod'
         path = 'path to some place'
-        with util.uncache(name):
-            with util.import_state(meta_path=[self.FakeMetaFinder]):
+        with test_util.uncache(name):
+            with test_util.import_state(meta_path=[self.FakeMetaFinder]):
                 with warnings.catch_warnings():
                     warnings.simplefilter('ignore', DeprecationWarning)
                     self.assertEqual((name, path),
@@ -171,11 +170,10 @@ class FindLoaderTests:
             warnings.simplefilter('ignore', DeprecationWarning)
             self.assertIsNone(self.init.find_loader('nevergoingtofindthismodule'))
 
-class Frozen_FindLoaderTests(FindLoaderTests, unittest.TestCase):
-    init = frozen_init
 
-class Source_FindLoaderTests(FindLoaderTests, unittest.TestCase):
-    init = source_init
+(Frozen_FindLoaderTests,
+ Source_FindLoaderTests
+ ) = test_util.test_both(FindLoaderTests, init=init)
 
 
 class ReloadTests:
@@ -195,10 +193,10 @@ class ReloadTests:
             module = type(sys)('top_level')
             module.spam = 3
             sys.modules['top_level'] = module
-        mock = util.mock_modules('top_level',
+        mock = test_util.mock_modules('top_level',
                                       module_code={'top_level': code})
         with mock:
-            with util.import_state(meta_path=[mock]):
+            with test_util.import_state(meta_path=[mock]):
                 module = self.init.import_module('top_level')
                 reloaded = self.init.reload(module)
                 actual = sys.modules['top_level']
@@ -230,7 +228,7 @@ class ReloadTests:
     def test_reload_location_changed(self):
         name = 'spam'
         with support.temp_cwd(None) as cwd:
-            with util.uncache('spam'):
+            with test_util.uncache('spam'):
                 with support.DirsOnSysPath(cwd):
                     # Start as a plain module.
                     self.init.invalidate_caches()
@@ -281,7 +279,7 @@ class ReloadTests:
     def test_reload_namespace_changed(self):
         name = 'spam'
         with support.temp_cwd(None) as cwd:
-            with util.uncache('spam'):
+            with test_util.uncache('spam'):
                 with support.DirsOnSysPath(cwd):
                     # Start as a namespace package.
                     self.init.invalidate_caches()
@@ -338,20 +336,16 @@ class ReloadTests:
         # See #19851.
         name = 'spam'
         subname = 'ham'
-        with util.temp_module(name, pkg=True) as pkg_dir:
-            fullname, _ = util.submodule(name, subname, pkg_dir)
+        with test_util.temp_module(name, pkg=True) as pkg_dir:
+            fullname, _ = test_util.submodule(name, subname, pkg_dir)
             ham = self.init.import_module(fullname)
             reloaded = self.init.reload(ham)
             self.assertIs(reloaded, ham)
 
 
-class Frozen_ReloadTests(ReloadTests, unittest.TestCase):
-    init = frozen_init
-    util = frozen_util
-
-class Source_ReloadTests(ReloadTests, unittest.TestCase):
-    init = source_init
-    util = source_util
+(Frozen_ReloadTests,
+ Source_ReloadTests
+ ) = test_util.test_both(ReloadTests, init=init, util=util)
 
 
 class InvalidateCacheTests:
@@ -384,11 +378,10 @@ class InvalidateCacheTests:
         self.addCleanup(lambda: sys.path_importer_cache.__delitem__(key))
         self.init.invalidate_caches()  # Shouldn't trigger an exception.
 
-class Frozen_InvalidateCacheTests(InvalidateCacheTests, unittest.TestCase):
-    init = frozen_init
 
-class Source_InvalidateCacheTests(InvalidateCacheTests, unittest.TestCase):
-    init = source_init
+(Frozen_InvalidateCacheTests,
+ Source_InvalidateCacheTests
+ ) = test_util.test_both(InvalidateCacheTests, init=init)
 
 
 class FrozenImportlibTests(unittest.TestCase):
@@ -398,6 +391,7 @@ class FrozenImportlibTests(unittest.TestCase):
         # Can't do an isinstance() check since separate copies of importlib
         # may have been used for import, so just check the name is not for the
         # frozen loader.
+        source_init = init['Source']
         self.assertNotEqual(source_init.__loader__.__class__.__name__,
                             'FrozenImporter')
 
@@ -426,11 +420,10 @@ class StartupTests:
                     elif self.machinery.FrozenImporter.find_module(name):
                         self.assertIsNot(module.__spec__, None)
 
-class Frozen_StartupTests(StartupTests, unittest.TestCase):
-    machinery = frozen_machinery
 
-class Source_StartupTests(StartupTests, unittest.TestCase):
-    machinery = source_machinery
+(Frozen_StartupTests,
+ Source_StartupTests
+ ) = test_util.test_both(StartupTests, machinery=machinery)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/test_locks.py

-from . import util
-frozen_init, source_init = util.import_importlib('importlib')
-frozen_bootstrap = frozen_init._bootstrap
-source_bootstrap = source_init._bootstrap
+from . import util as test_util
+
+init = test_util.import_importlib('importlib')
 
 import sys
 import time
@@ -33,13 +32,16 @@ if threading is not None:
         # _release_save() unsupported
         test_release_save_unacquired = None
 
-    class Frozen_ModuleLockAsRLockTests(ModuleLockAsRLockTests, lock_tests.RLockTests):
-        LockType = frozen_bootstrap._ModuleLock
-
-    class Source_ModuleLockAsRLockTests(ModuleLockAsRLockTests, lock_tests.RLockTests):
-        LockType = source_bootstrap._ModuleLock
+    LOCK_TYPES = {kind: splitinit._bootstrap._ModuleLock
+                  for kind, splitinit in init.items()}
 
+    (Frozen_ModuleLockAsRLockTests,
+     Source_ModuleLockAsRLockTests
+     ) = test_util.test_both(ModuleLockAsRLockTests, lock_tests.RLockTests,
+                             LockType=LOCK_TYPES)
 else:
+    LOCK_TYPES = {}
+
     class Frozen_ModuleLockAsRLockTests(unittest.TestCase):
         pass
 
@@ -47,6 +49,7 @@ else:
         pass
 
 
+@unittest.skipUnless(threading, "threads needed for this test")
 class DeadlockAvoidanceTests:
 
     def setUp(self):
@@ -106,19 +109,22 @@ class DeadlockAvoidanceTests:
         self.assertEqual(results.count((True, False)), 0)
         self.assertEqual(results.count((True, True)), len(results))
 
-@unittest.skipUnless(threading, "threads needed for this test")
-class Frozen_DeadlockAvoidanceTests(DeadlockAvoidanceTests, unittest.TestCase):
-    LockType = frozen_bootstrap._ModuleLock
-    DeadlockError = frozen_bootstrap._DeadlockError
 
-@unittest.skipUnless(threading, "threads needed for this test")
-class Source_DeadlockAvoidanceTests(DeadlockAvoidanceTests, unittest.TestCase):
-    LockType = source_bootstrap._ModuleLock
-    DeadlockError = source_bootstrap._DeadlockError
+DEADLOCK_ERRORS = {kind: splitinit._bootstrap._DeadlockError
+                   for kind, splitinit in init.items()}
+
+(Frozen_DeadlockAvoidanceTests,
+ Source_DeadlockAvoidanceTests
+ ) = test_util.test_both(DeadlockAvoidanceTests,
+                         LockType=LOCK_TYPES, DeadlockError=DEADLOCK_ERRORS)
 
 
 class LifetimeTests:
 
+    @property
+    def bootstrap(self):
+        return self.init._bootstrap
+
     def test_lock_lifetime(self):
         name = "xyzzy"
         self.assertNotIn(name, self.bootstrap._module_locks)
@@ -135,11 +141,10 @@ class LifetimeTests:
         self.assertEqual(0, len(self.bootstrap._module_locks),
                          self.bootstrap._module_locks)
 
-class Frozen_LifetimeTests(LifetimeTests, unittest.TestCase):
-    bootstrap = frozen_bootstrap
 
-class Source_LifetimeTests(LifetimeTests, unittest.TestCase):
-    bootstrap = source_bootstrap
+(Frozen_LifetimeTests,
+ Source_LifetimeTests
+ ) = test_util.test_both(LifetimeTests, init=init)
 
 
 @support.reap_threads

Lib/test/test_importlib/test_spec.py

-from . import util
+from . import util as test_util
 
-frozen_init, source_init = util.import_importlib('importlib')
-frozen_bootstrap = frozen_init._bootstrap
-source_bootstrap = source_init._bootstrap
-frozen_machinery, source_machinery = util.import_importlib('importlib.machinery')
-frozen_util, source_util = util.import_importlib('importlib.util')
+init = test_util.import_importlib('importlib')
+machinery = test_util.import_importlib('importlib.machinery')
+util = test_util.import_importlib('importlib.util')
 
 import os.path
 from test.support import CleanImport
@@ -52,6 +50,8 @@ class LegacyLoader(TestLoader):
     with warnings.catch_warnings():
         warnings.simplefilter("ignore", DeprecationWarning)
 
+        frozen_util = util['Frozen']
+
         @frozen_util.module_for_loader
         def load_module(self, module):
             module.ham = self.HAM
@@ -221,18 +221,17 @@ class ModuleSpecTests:
         self.assertEqual(self.loc_spec.cached, 'spam.pyc')
 
 
-class Frozen_ModuleSpecTests(ModuleSpecTests, unittest.TestCase):
-    util = frozen_util
-    machinery = frozen_machinery
-
-
-class Source_ModuleSpecTests(ModuleSpecTests, unittest.TestCase):
-    util = source_util
-    machinery = source_machinery
+(Frozen_ModuleSpecTests,
+ Source_ModuleSpecTests
+ ) = test_util.test_both(ModuleSpecTests, util=util, machinery=machinery)
 
 
 class ModuleSpecMethodsTests:
 
+    @property
+    def bootstrap(self):
+        return self.init._bootstrap
+
     def setUp(self):
         self.name = 'spam'
         self.path = 'spam.py'
@@ -528,20 +527,18 @@ class ModuleSpecMethodsTests:
         self.assertIs(installed, loaded)
 
 
-class Frozen_ModuleSpecMethodsTests(ModuleSpecMethodsTests, unittest.TestCase):
-    bootstrap = frozen_bootstrap
-    machinery = frozen_machinery
-    util = frozen_util
-
-
-class Source_ModuleSpecMethodsTests(ModuleSpecMethodsTests, unittest.TestCase):
-    bootstrap = source_bootstrap
-    machinery = source_machinery
-    util = source_util
+(Frozen_ModuleSpecMethodsTests,
+ Source_ModuleSpecMethodsTests
+ ) = test_util.test_both(ModuleSpecMethodsTests, init=init, util=util,
+                         machinery=machinery)
 
 
 class ModuleReprTests:
 
+    @property
+    def bootstrap(self):
+        return self.init._bootstrap
+
     def setUp(self):
         self.module = type(os)('spam')
         self.spec = self.machinery.ModuleSpec('spam', TestLoader())
@@ -625,16 +622,10 @@ class ModuleReprTests:
         self.assertEqual(modrepr, '<module {!r}>'.format('spam'))
 
 
-class Frozen_ModuleReprTests(ModuleReprTests, unittest.TestCase):
-    bootstrap = frozen_bootstrap
-    machinery = frozen_machinery
-    util = frozen_util
-
-
-class Source_ModuleReprTests(ModuleReprTests, unittest.TestCase):
-    bootstrap = source_bootstrap
-    machinery = source_machinery
-    util = source_util
+(Frozen_ModuleReprTests,
+ Source_ModuleReprTests
+ ) = test_util.test_both(ModuleReprTests, init=init, util=util,
+                         machinery=machinery)
 
 
 class FactoryTests:
@@ -787,7 +778,7 @@ class FactoryTests:
     # spec_from_file_location()
 
     def test_spec_from_file_location_default(self):
-        if self.machinery is source_machinery:
+        if self.machinery is machinery['Source']:
             raise unittest.SkipTest('not sure why this is breaking...')
         spec = self.util.spec_from_file_location(self.name, self.path)
 
@@ -947,11 +938,6 @@ class FactoryTests:
         self.assertTrue(spec.has_location)
 
 
-class Frozen_FactoryTests(FactoryTests, unittest.TestCase):
-    util = frozen_util
-    machinery = frozen_machinery
-
-
-class Source_FactoryTests(FactoryTests, unittest.TestCase):
-    util = source_util
-    machinery = source_machinery
+(Frozen_FactoryTests,
+ Source_FactoryTests
+ ) = test_util.test_both(FactoryTests, util=util, machinery=machinery)

Lib/test/test_importlib/test_util.py

-from importlib import util
+import importlib.util
 from . import util as test_util
-frozen_init, source_init = test_util.import_importlib('importlib')
-frozen_machinery, source_machinery = test_util.import_importlib('importlib.machinery')
-frozen_util, source_util = test_util.import_importlib('importlib.util')
+init = test_util.import_importlib('importlib')
+machinery = test_util.import_importlib('importlib.machinery')
+util = test_util.import_importlib('importlib.util')
 
 import os
 import sys
@@ -32,8 +32,10 @@ class DecodeSourceBytesTests:
         self.assertEqual(self.util.decode_source(source_bytes),
                          '\n'.join([self.source, self.source]))
 
-Frozen_DecodeSourceBytesTests, Source_DecodeSourceBytesTests = test_util.test_both(
-        DecodeSourceBytesTests, util=[frozen_util, source_util])
+
+(Frozen_DecodeSourceBytesTests,
+ Source_DecodeSourceBytesTests
+ ) = test_util.test_both(DecodeSourceBytesTests, util=util)
 
 
 class ModuleForLoaderTests:
@@ -161,8 +163,10 @@ class ModuleForLoaderTests:
             self.assertIs(module.__loader__, loader)
             self.assertEqual(module.__package__, name)
 
-Frozen_ModuleForLoaderTests, Source_ModuleForLoaderTests = test_util.test_both(
-        ModuleForLoaderTests, util=[frozen_util, source_util])
+
+(Frozen_ModuleForLoaderTests,
+ Source_ModuleForLoaderTests
+ ) = test_util.test_both(ModuleForLoaderTests, util=util)
 
 
 class SetPackageTests:
@@ -222,18 +226,25 @@ class SetPackageTests:
         self.assertEqual(wrapped.__name__, fxn.__name__)
         self.assertEqual(wrapped.__qualname__, fxn.__qualname__)
 
-Frozen_SetPackageTests, Source_SetPackageTests = test_util.test_both(
-        SetPackageTests, util=[frozen_util, source_util])
+
+(Frozen_SetPackageTests,
+ Source_SetPackageTests
+ ) = test_util.test_both(SetPackageTests, util=util)
 
 
 class SetLoaderTests:
 
     """Tests importlib.util.set_loader()."""
 
+    @property
+    def DummyLoader(self):
+        # Set DummyLoader on the class lazily.
         class DummyLoader:
-        @util.set_loader
+            @self.util.set_loader
             def load_module(self, module):
                 return self.module
+        self.__class__.DummyLoader = DummyLoader
+        return DummyLoader
 
     def test_no_attribute(self):
         loader = self.DummyLoader()
@@ -262,17 +273,10 @@ class SetLoaderTests:
             warnings.simplefilter('ignore', DeprecationWarning)
             self.assertEqual(42, loader.load_module('blah').__loader__)
 
-class Frozen_SetLoaderTests(SetLoaderTests, unittest.TestCase):
-    class DummyLoader:
-        @frozen_util.set_loader
-        def load_module(self, module):
-            return self.module
 
-class Source_SetLoaderTests(SetLoaderTests, unittest.TestCase):
-    class DummyLoader:
-        @source_util.set_loader
-        def load_module(self, module):
-            return self.module
+(Frozen_SetLoaderTests,
+ Source_SetLoaderTests
+ ) = test_util.test_both(SetLoaderTests, util=util)
 
 
 class ResolveNameTests:
@@ -307,9 +311,10 @@ class ResolveNameTests:
         with self.assertRaises(ValueError):
             self.util.resolve_name('..bacon', 'spam')
 
-Frozen_ResolveNameTests, Source_ResolveNameTests = test_util.test_both(
-        ResolveNameTests,
-        util=[frozen_util, source_util])
+
+(Frozen_ResolveNameTests,
+ Source_ResolveNameTests
+ ) = test_util.test_both(ResolveNameTests, util=util)
 
 
 class FindSpecTests:
@@ -446,15 +451,10 @@ class FindSpecTests:
             self.assertNotIn(fullname, sorted(sys.modules))
 
 
-class Frozen_FindSpecTests(FindSpecTests, unittest.TestCase):
-    init = frozen_init
-    machinery = frozen_machinery
-    util = frozen_util
-
-class Source_FindSpecTests(FindSpecTests, unittest.TestCase):
-    init = source_init
-    machinery = source_machinery
-    util = source_util
+(Frozen_FindSpecTests,
+ Source_FindSpecTests
+ ) = test_util.test_both(FindSpecTests, init=init, util=util,
+                         machinery=machinery)
 
 
 class MagicNumberTests:
@@ -467,8 +467,10 @@ class MagicNumberTests:
         # The magic number uses \r\n to come out wrong when splitting on lines.
         self.assertTrue(self.util.MAGIC_NUMBER.endswith(b'\r\n'))
 
-Frozen_MagicNumberTests, Source_MagicNumberTests = test_util.test_both(
-        MagicNumberTests, util=[frozen_util, source_util])
+
+(Frozen_MagicNumberTests,
+ Source_MagicNumberTests
+ ) = test_util.test_both(MagicNumberTests, util=util)
 
 
 class PEP3147Tests:
@@ -583,9 +585,10 @@ class PEP3147Tests:
             ValueError, self.util.source_from_cache,
             '/foo/bar/foo.cpython-32.foo.pyc')
 
-Frozen_PEP3147Tests, Source_PEP3147Tests = test_util.test_both(
-        PEP3147Tests,
-        util=[frozen_util, source_util])
+
+(Frozen_PEP3147Tests,
+ Source_PEP3147Tests
+ ) = test_util.test_both(PEP3147Tests, util=util)
 
 
 if __name__ == '__main__':

Lib/test/test_importlib/test_windows.py

-from . import util
-frozen_machinery, source_machinery = util.import_importlib('importlib.machinery')
+from . import util as test_util
+machinery = test_util.import_importlib('importlib.machinery')
 
 import sys
 import unittest
@@ -19,11 +19,6 @@ class WindowsRegistryFinderTests:
         self.assertIs(loader, None)
 
 
-class Frozen_WindowsRegistryFinderTests(WindowsRegistryFinderTests,
-                                        unittest.TestCase):
-    machinery = frozen_machinery
-
-
-class Source_WindowsRegistryFinderTests(WindowsRegistryFinderTests,
-                                        unittest.TestCase):
-    machinery = source_machinery
+(Frozen_WindowsRegistryFinderTests,
+ Source_WindowsRegistryFinderTests
+ ) = test_util.test_both(WindowsRegistryFinderTests, machinery=machinery)

Lib/test/test_importlib/util.py

@@ -50,19 +50,36 @@ def import_importlib(module_name):
     frozen = support.import_fresh_module(module_name)
     source = support.import_fresh_module(module_name, fresh=fresh,
                                          blocked=('_frozen_importlib',))
+    return {'Frozen': frozen, 'Source': source}
+
+
+def specialize_class(cls, kind, base=None, **kwargs):
+    # XXX Support passing in submodule names--load (and cache) them?
+    # That would clean up the test modules a bit more.
+    if base is None:
+        base = unittest.TestCase
+    elif not isinstance(base, type):
+        base = base[kind]
+    name = '{}_{}'.format(kind, cls.__name__)
+    bases = (cls, base)
+    specialized = types.new_class(name, bases)
+    specialized.__module__ = cls.__module__
+    specialized._NAME = cls.__name__
+    specialized._KIND = kind
+    for attr, values in kwargs.items():
+        value = values[kind]
+        setattr(specialized, attr, value)
+    return specialized
+
+
+def split_frozen(cls, base=None, **kwargs):
+    frozen = specialize_class(cls, 'Frozen', base, **kwargs)
+    source = specialize_class(cls, 'Source', base, **kwargs)
     return frozen, source
 
 
-def test_both(test_class, **kwargs):
-    frozen_tests = types.new_class('Frozen_'+test_class.__name__,
-                                   (test_class, unittest.TestCase))
-    source_tests = types.new_class('Source_'+test_class.__name__,
-                                   (test_class, unittest.TestCase))
-    frozen_tests.__module__ = source_tests.__module__ = test_class.__module__
-    for attr, (frozen_value, source_value) in kwargs.items():
-        setattr(frozen_tests, attr, frozen_value)
-        setattr(source_tests, attr, source_value)
-    return frozen_tests, source_tests
+def test_both(test_class, base=None, **kwargs):
+    return split_frozen(test_class, base, **kwargs)
 
 
 CASE_INSENSITIVE_FS = True
@@ -75,8 +92,9 @@ if sys.platform not in ('win32', 'cygwin'):
     if not os.path.exists(changed_name):
         CASE_INSENSITIVE_FS = False
 
-_, source_importlib = import_importlib('importlib')
-__import__ = staticmethod(builtins.__import__), staticmethod(source_importlib.__import__)
+source_importlib = import_importlib('importlib')['Source']
+__import__ = {'Frozen': staticmethod(builtins.__import__),
+              'Source': staticmethod(source_importlib.__import__)}
 
 
 def case_insensitive_tests(test):

Misc/NEWS

@@ -496,6 +496,8 @@ Tests
 
 - Issue #21097: Move test_namespace_pkgs into test_importlib.
 
+- Issue #21503: Use test_both() consistently in test_importlib.
+
 - Issue #20939: Avoid various network test failures due to new
   redirect of http://www.python.org/ to https://www.python.org:
   use http://www.example.com instead.