Refactor: move `no_rerun` from `test_import` and `datetimetester` to `test.support`

[sobolevn]

Feature or enhancement

It is defined here:

cpython/Lib/test/test_import/__init__.py

Lines 123 to 139 in b407ad3

	def no_rerun(reason):
	"""Skip rerunning for a particular test.
	WARNING: Use this decorator with care; skipping rerunning makes it
	impossible to find reference leaks. Provide a clear reason for skipping the
	test using the 'reason' parameter.
	"""
	def deco(func):
	_has_run = False
	def wrapper(self):
	nonlocal _has_run
	if _has_run:
	self.skipTest(reason)
	func(self)
	_has_run = True
	return wrapper
	return deco

and here:

cpython/Lib/test/datetimetester.py

Lines 50 to 68 in b407ad3

	# This is copied from test_import/__init__.py.
	# XXX Move it to support/__init__.py.
	def no_rerun(reason):
	"""Skip rerunning for a particular test.
	WARNING: Use this decorator with care; skipping rerunning makes it
	impossible to find reference leaks. Provide a clear reason for skipping the
	test using the 'reason' parameter.
	"""
	def deco(func):
	_has_run = False
	def wrapper(self):
	nonlocal _has_run
	if _has_run:
	self.skipTest(reason)
	func(self)
	_has_run = True
	return wrapper
	return deco

Introduced in #119373

Linked PRs

• gh-119659: Move @no_rerun to test.support #119660
• gh-119659: Fix support.no_rerun decorator #119675
• gh-119659: Get the datetime CAPI Tests Running Again #120180

[sobolevn]

aaaand I found a bug:

cpython/Lib/test/support/__init__.py

Lines 1192 to 1208 in 0518edc

	def no_rerun(reason):
	"""Skip rerunning for a particular test.
	WARNING: Use this decorator with care; skipping rerunning makes it
	impossible to find reference leaks. Provide a clear reason for skipping the
	test using the 'reason' parameter.
	"""
	def deco(func):
	_has_run = False
	def wrapper(self):
	nonlocal _has_run
	if _has_run:
	self.skipTest(reason)
	func(self)
	_has_run = True
	return wrapper
	return deco

this code does not work well when applied to classes.

proof (with @no_rerun decorator):

cpython/Lib/test/datetimetester.py

Lines 6385 to 6392 in 0518edc

	@unittest.skipIf(_testcapi is None, 'need _testcapi module')
	@no_rerun("the encapsulated datetime C API does not support reloading")
	class CapiTest(unittest.TestCase):
	def setUp(self):
	# Since the C API is not present in the _Pure tests, skip all tests
	if self.__class__.__name__.endswith('Pure'):
	self.skipTest('Not relevant in pure Python')

» ./python.exe -m test test_datetime -m test_utc_capi -v
== CPython 3.14.0a0 (heads/main:669175bf8ed, May 28 2024, 13:18:18) [Clang 15.0.0 (clang-1500.3.9.4)]
== macOS-14.4.1-arm64-arm-64bit-Mach-O little-endian
== Python build: debug
== cwd: /Users/sobolev/Desktop/cpython2/build/test_python_worker_98352æ
== CPU count: 12
== encodings: locale=UTF-8 FS=utf-8
== resources: all test resources are disabled, use -u option to unskip tests

Using random seed: 1630075014
0:00:00 load avg: 2.16 Run 1 test sequentially
0:00:00 load avg: 2.16 [1/1] test_datetime

----------------------------------------------------------------------
Ran 0 tests in 0.000s

NO TESTS RAN
test_datetime ran no tests

== Tests result: NO TESTS RAN ==

1 test run no tests:
 test_datetime

Total duration: 124 ms
Total tests: run=0 (filtered)
Total test files: run=1/1 (filtered) run_no_tests=1
Result: NO TESTS RAN

Without:

» ./python.exe -m test test_datetime -m test_utc_capi -v
== CPython 3.14.0a0 (heads/main:669175bf8ed, May 28 2024, 13:18:18) [Clang 15.0.0 (clang-1500.3.9.4)]
== macOS-14.4.1-arm64-arm-64bit-Mach-O little-endian
== Python build: debug
== cwd: /Users/sobolev/Desktop/cpython2/build/test_python_worker_98457æ
== CPU count: 12
== encodings: locale=UTF-8 FS=utf-8
== resources: all test resources are disabled, use -u option to unskip tests

Using random seed: 1077352783
0:00:00 load avg: 1.75 Run 1 test sequentially
0:00:00 load avg: 1.75 [1/1] test_datetime
test_utc_capi (test.datetimetester.CapiTest_Pure.test_utc_capi) ... skipped 'Not relevant in pure Python'
test_utc_capi (test.datetimetester.CapiTest_Fast.test_utc_capi) ... ok

----------------------------------------------------------------------
Ran 2 tests in 0.000s

OK (skipped=1)

== Tests result: SUCCESS ==

1 test OK.

Total duration: 130 ms
Total tests: run=2 (filtered) skipped=1
Total test files: run=1/1 (filtered)
Result: SUCCESS

Turns out it is not just "moving", I also have to fix it for both types and methods.

[sobolevn]

Aaaand I found another one: test_datetime forgets about existing setUpClass and tearDownClass:

cpython/Lib/test/test_datetime.py

Lines 39 to 56 in 0518edc

	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
	tests.addTests(loader.loadTestsFromTestCase(cls))

[sobolevn]

And the whole nonlocal _has_run idea simply does not work 🙈
Because on each run the test class is different.

Wow, what a ride! 😄