test_datetime does not respect custom setUpClass and tearDownClass

[sobolevn]

Bug report

Example test case that can be possibly added to test_datetime.py:

class TestExample(unittest.TestCase):
    @classmethod
    def setUpClass(cls) -> None:
        cls.value_to_test = 1
        return super().setUpClass()

    def test_example_bug(self):
        self.assertEqual(self.value_to_test, 1)

./python.exe -m test test_datetime -v -m test_example_bug outputs:

test_example_bug (test.datetimetester.TestExample_Pure.test_example_bug) ... ERROR
test_example_bug (test.datetimetester.TestExample_Fast.test_example_bug) ... ERROR

======================================================================
ERROR: test_example_bug (test.datetimetester.TestExample_Pure.test_example_bug)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython2/Lib/test/datetimetester.py", line 77, in test_example_bug
    self.assertEqual(self.value_to_test, 1)
                     ^^^^^^^^^^^^^^^^^^
AttributeError: 'TestExample_Pure' object has no attribute 'value_to_test'

======================================================================
ERROR: test_example_bug (test.datetimetester.TestExample_Fast.test_example_bug)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/sobolev/Desktop/cpython2/Lib/test/datetimetester.py", line 77, in test_example_bug
    self.assertEqual(self.value_to_test, 1)
                     ^^^^^^^^^^^^^^^^^^
AttributeError: 'TestExample_Fast' object has no attribute 'value_to_test'

----------------------------------------------------------------------
Ran 2 tests in 0.003s

FAILED (errors=2)
test test_datetime failed
test_datetime failed (2 errors)

== Tests result: FAILURE ==

1 test failed:
    test_datetime

Total duration: 208 ms
Total tests: run=2 (filtered)
Total test files: run=1/1 (filtered) failed=1
Result: FAILURE

This happens because of these lines:

cpython/Lib/test/test_datetime.py

Lines 39 to 55 in e6076d1

	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
	if hasattr(module, '_pydatetime'):
	sys.modules['_pydatetime'] = module._pydatetime
	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

I proposed this fix: https://github.com/python/cpython/pull/119675/files#diff-d4ea73ff6f3d1428ce4536793404e64ce7dbc1f6d0afe22f707ee0a24777afea but it was not merged.

Refs #119675
Refs #119659

Linked PRs

• gh-120242: Fix handling of [setUp,tearDown]Class in test_datetime #120243
• [3.13] gh-120242: Fix handling of [setUp,tearDown]Class in test_datetime (GH-120243) #120259
• [3.12] gh-120242: Fix handling of [setUp,tearDown]Class in test_datetime (GH-120243) #120260