Running test_dataclasses file directly fails

[wookie184]

Bug report

Running ./python Lib/test/test_dataclasses.py gives me these test fails:

[root@codespaces-44977f cpython]# ./python Lib/test/test_dataclasses.py
....................................................................................................................................................................................EEEEEE...................................................
======================================================================
ERROR: test_pickle_support (__main__.TestMakeDataclass.test_pickle_support) (proto=0)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/workspaces/cpython/Lib/test/test_dataclasses.py", line 3802, in test_pickle_support
    pickle.loads(pickle.dumps(klass, proto)),
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^
_pickle.PicklingError: Can't pickle <class 'test.test_dataclasses.ManualModuleMakeDataClass'>: it's not the same object as test.test_dataclasses.ManualModuleMakeDataClass

======================================================================
ERROR: test_pickle_support (__main__.TestMakeDataclass.test_pickle_support) (proto=1)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/workspaces/cpython/Lib/test/test_dataclasses.py", line 3802, in test_pickle_support
    pickle.loads(pickle.dumps(klass, proto)),
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^
_pickle.PicklingError: Can't pickle <class 'test.test_dataclasses.ManualModuleMakeDataClass'>: it's not the same object as test.test_dataclasses.ManualModuleMakeDataClass

======================================================================
ERROR: test_pickle_support (__main__.TestMakeDataclass.test_pickle_support) (proto=2)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/workspaces/cpython/Lib/test/test_dataclasses.py", line 3802, in test_pickle_support
    pickle.loads(pickle.dumps(klass, proto)),
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^
_pickle.PicklingError: Can't pickle <class 'test.test_dataclasses.ManualModuleMakeDataClass'>: it's not the same object as test.test_dataclasses.ManualModuleMakeDataClass

======================================================================
ERROR: test_pickle_support (__main__.TestMakeDataclass.test_pickle_support) (proto=3)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/workspaces/cpython/Lib/test/test_dataclasses.py", line 3802, in test_pickle_support
    pickle.loads(pickle.dumps(klass, proto)),
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^
_pickle.PicklingError: Can't pickle <class 'test.test_dataclasses.ManualModuleMakeDataClass'>: it's not the same object as test.test_dataclasses.ManualModuleMakeDataClass

======================================================================
ERROR: test_pickle_support (__main__.TestMakeDataclass.test_pickle_support) (proto=4)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/workspaces/cpython/Lib/test/test_dataclasses.py", line 3802, in test_pickle_support
    pickle.loads(pickle.dumps(klass, proto)),
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^
_pickle.PicklingError: Can't pickle <class 'test.test_dataclasses.ManualModuleMakeDataClass'>: it's not the same object as test.test_dataclasses.ManualModuleMakeDataClass

======================================================================
ERROR: test_pickle_support (__main__.TestMakeDataclass.test_pickle_support) (proto=5)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/workspaces/cpython/Lib/test/test_dataclasses.py", line 3802, in test_pickle_support
    pickle.loads(pickle.dumps(klass, proto)),
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^
_pickle.PicklingError: Can't pickle <class 'test.test_dataclasses.ManualModuleMakeDataClass'>: it's not the same object as test.test_dataclasses.ManualModuleMakeDataClass

----------------------------------------------------------------------
Ran 232 tests in 0.408s

FAILED (errors=6)

When running ./python -m test test_dataclasses, the tests all pass successfully. My understanding is that python -m test is the recommended way of running tests, but it's confusing to have it support running the file directly, but have the tests fail.

I'm not sure what the cause of the failure is.

Your environment

• CPython versions tested on: main (ed95e8c)
• Operating system and architecture: GitHub Codespaces

Linked PRs

• gh-104015: Fix direct invocation of test_dataclasses #104017

[AlexWaygood]

The problematic tests were added relatively recently, in b48be8f (cc. @sobolevn)

[sobolevn]

I will take a look, thanks!