test: regression test for #403 (mock.patch.dict + asyncio_mode=auto)

[mvanhorn]

Summary

#403 reported that async tests decorated with unittest.mock.patch.dict were silently skipped under asyncio_mode=auto, surfaced as a PytestUnhandledCoroutineWarning. The root cause was a CPython bug in how iscoroutinefunction unwrapped patch.dict. seifertm filed python/cpython#98086 and the fix was backported to CPython 3.10 (and 3.11). pytest-asyncio now requires Python >= 3.10, so the scenario is no longer reachable.

This PR adds a regression test in tests/modes/test_auto_mode.py to lock that property in. The test reproduces the issue's two failing variants - test_doesnt_run (only decorated with @mock.patch.dict) and test_runs_anyway (also explicitly marked @pytest.mark.asyncio) - and asserts both are collected and pass under --asyncio-mode=auto. If a future refactor reintroduces the unwrapping bug at this layer (e.g. switching back to a iscoroutinefunction call that doesn't see through patch.dict), this test fails immediately.

Files

• tests/modes/test_auto_mode.py: new test_auto_mode_async_test_with_mock_patch_dict test
• changelog.d/403.fixed.rst: news fragment

Verification

$ pytest tests/modes/test_auto_mode.py -v
...
tests/modes/test_auto_mode.py::test_auto_mode_cmdline PASSED             [ 14%]
tests/modes/test_auto_mode.py::test_auto_mode_cfg PASSED                 [ 28%]
tests/modes/test_auto_mode.py::test_auto_mode_async_fixture PASSED       [ 42%]
tests/modes/test_auto_mode.py::test_auto_mode_method_fixture PASSED      [ 57%]
tests/modes/test_auto_mode.py::test_auto_mode_static_method PASSED       [ 71%]
tests/modes/test_auto_mode.py::test_auto_mode_static_method_fixture PASSED [ 85%]
tests/modes/test_auto_mode.py::test_auto_mode_async_test_with_mock_patch_dict PASSED [100%]
============================== 7 passed in 0.11s ===============================

Also verified the original repro from the issue body runs cleanly under Python 3.14.3 + current pytest-asyncio main (3/3 passed), confirming the CPython backport is the right reason this test passes today rather than a workaround in this repo.

Closes #403

AI disclosure: regression test and PR body drafted with Claude as a coding assistant; I ran the tests and reviewed the changes before pushing.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.50%. Comparing base (7582774) to head (5ec917f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1443   +/-   ##
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  Coverage   94.50%   94.50%           
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  Files           2        2           
  Lines         510      510           
  Branches       62       62           
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  Hits          482      482           
  Misses         22       22           
  Partials        6        6           

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[seifertm]

Thanks for the initiative, @mvanhorn .

I wish I could give a different response, but I don't want to merge the code. The PR adds a test for a bug that occurred in a CPython module of a Python version that is no longer supported by pytest-asyncio. I understand that the issue originally surfaced in pytest-asyncio, but it's not realistic to test every possible interaction with other libraries or modules. Nor is it desired, since test code also needs to be maintained. This particular patch doesn't contribute to test coverage either, so I'm closing this PR.

I'm happy to discuss this further and be swayed, if you can convince me otherwise.