[3.9] bpo-45229: Make datetime tests discoverable (GH-28615). (GH-28645)

(cherry picked from commit d441437)

Author: serhiy-storchaka

Lib/test/test_datetime.py

@@ -1,57 +1,57 @@
 import unittest
 import sys
 
-from test.support import import_fresh_module, run_unittest
+from test.support import import_fresh_module
+
 
 TESTS = 'test.datetimetester'
 
-try:
-    pure_tests = import_fresh_module(TESTS, fresh=['datetime', '_strptime'],
-                                     blocked=['_datetime'])
-    fast_tests = import_fresh_module(TESTS, fresh=['datetime',
-                                                   '_datetime', '_strptime'])
-finally:
-    # XXX: import_fresh_module() is supposed to leave sys.module cache untouched,
-    # XXX: but it does not, so we have to cleanup ourselves.
-    for modname in ['datetime', '_datetime', '_strptime']:
-        sys.modules.pop(modname, None)
-test_modules = [pure_tests, fast_tests]
-test_suffixes = ["_Pure", "_Fast"]
-# XXX(gb) First run all the _Pure tests, then all the _Fast tests.  You might
-# not believe this, but in spite of all the sys.modules trickery running a _Pure
-# test last will leave a mix of pure and native datetime stuff lying around.
-all_test_classes = []
+def load_tests(loader, tests, pattern):
+    try:
+        pure_tests = import_fresh_module(TESTS, fresh=['datetime', '_strptime'],
+                                        blocked=['_datetime'])
+        fast_tests = import_fresh_module(TESTS, fresh=['datetime',
+                                                    '_datetime', '_strptime'])
+    finally:
+        # XXX: import_fresh_module() is supposed to leave sys.module cache untouched,
+        # XXX: but it does not, so we have to cleanup ourselves.
+        for modname in ['datetime', '_datetime', '_strptime']:
+            sys.modules.pop(modname, None)
 
-for module, suffix in zip(test_modules, test_suffixes):
-    test_classes = []
-    for name, cls in module.__dict__.items():
-        if not isinstance(cls, type):
-            continue
-        if issubclass(cls, unittest.TestCase):
-            test_classes.append(cls)
-        elif issubclass(cls, unittest.TestSuite):
-            suit = cls()
-            test_classes.extend(type(test) for test in suit)
-    test_classes = sorted(set(test_classes), key=lambda cls: cls.__qualname__)
-    for cls in test_classes:
-        cls.__name__ += suffix
-        cls.__qualname__ += suffix
-        @classmethod
-        def setUpClass(cls_, module=module):
-            cls_._save_sys_modules = sys.modules.copy()
-            sys.modules[TESTS] = module
-            sys.modules['datetime'] = module.datetime_module
-            sys.modules['_strptime'] = module._strptime
-        @classmethod
-        def tearDownClass(cls_):
-            sys.modules.clear()
-            sys.modules.update(cls_._save_sys_modules)
-        cls.setUpClass = setUpClass
-        cls.tearDownClass = tearDownClass
-    all_test_classes.extend(test_classes)
+    test_modules = [pure_tests, fast_tests]
+    test_suffixes = ["_Pure", "_Fast"]
+    # XXX(gb) First run all the _Pure tests, then all the _Fast tests.  You might
+    # not believe this, but in spite of all the sys.modules trickery running a _Pure
+    # test last will leave a mix of pure and native datetime stuff lying around.
+    for module, suffix in zip(test_modules, test_suffixes):
+        test_classes = []
+        for name, cls in module.__dict__.items():
+            if not isinstance(cls, type):
+                continue
+            if issubclass(cls, unittest.TestCase):
+                test_classes.append(cls)
+            elif issubclass(cls, unittest.TestSuite):
+                suit = cls()
+                test_classes.extend(type(test) for test in suit)
+        test_classes = sorted(set(test_classes), key=lambda cls: cls.__qualname__)
+        for cls in test_classes:
+            cls.__name__ += suffix
+            cls.__qualname__ += suffix
+            @classmethod
+            def setUpClass(cls_, module=module):
+                cls_._save_sys_modules = sys.modules.copy()
+                sys.modules[TESTS] = module
+                sys.modules['datetime'] = module.datetime_module
+                sys.modules['_strptime'] = module._strptime
+            @classmethod
+            def tearDownClass(cls_):
+                sys.modules.clear()
+                sys.modules.update(cls_._save_sys_modules)
+            cls.setUpClass = setUpClass
+            cls.tearDownClass = tearDownClass
+            tests.addTests(loader.loadTestsFromTestCase(cls))
+    return tests
 
-def test_main():
-    run_unittest(*all_test_classes)
 
 if __name__ == "__main__":
-    test_main()
+    unittest.main()