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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