Fix event_loop_policy parametrization scope

[puneetdixit200]

Summary

• stop making the default event_loop_policy fixture autouse
• request event_loop_policy only for pytest-asyncio tests and tests using asyncio fixtures, so plain sync tests are not parametrized
• add regression coverage for plain sync tests and sync tests that use asyncio fixtures
• avoid re-importing pytest_asyncio in one subprocess test under -W error; the entry point already loads the plugin

Fixes #796

Tests

• .venv/bin/python -m pytest -q
• .venv/bin/python -m pytest tests/test_set_event_loop.py::test_asyncio_run_after_async_fixture_does_not_leak_loop tests/markers/test_function_scope.py::test_parametrized_loop_policy_does_not_parametrize_sync_tests tests/markers/test_function_scope.py::test_parametrized_loop_policy_parametrizes_sync_tests_with_async_fixtures -q
• .venv/bin/python -m pytest tests/markers/test_function_scope.py tests/markers/test_module_scope.py tests/markers/test_class_scope.py tests/markers/test_session_scope.py tests/test_loop_factory_parametrization.py tests/test_asyncio_fixture.py -q
• .venv/bin/python -m ruff check pytest_asyncio/plugin.py tests/markers/test_function_scope.py tests/test_set_event_loop.py
• .venv/bin/python -m mypy --python-version 3.13 pytest_asyncio/
• .venv/bin/python -m pyright --pythonpath .venv/bin/python --pythonversion 3.13 pytest_asyncio/
• git diff --check

[codecov-commenter]

Codecov Report

❌ Patch coverage is 85.18519% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.00%. Comparing base (9190447) to head (8305b3a).

Files with missing lines	Patch %	Lines
pytest_asyncio/plugin.py	85.18%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1454      +/-   ##
==========================================
- Coverage   94.50%   94.00%   -0.51%     
==========================================
  Files           2        2              
  Lines         510      534      +24     
  Branches       62       69       +7     
==========================================
+ Hits          482      502      +20     
- Misses         22       24       +2     
- Partials        6        8       +2     

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[golikovichev]

Approach looks clean. Dropping autouse=True from the event_loop_policy fixture and gating its injection on pytest_generate_tests only when the test uses asyncio fixtures (or is async itself) is the right shape to fix #796 without breaking the loop-policy parametrization use case.

Two observations from a downstream-user read:

1. _uses_asyncio_fixtures walks metafunc._arg2fixturedefs and short-circuits on first match. In AUTO mode it falls back to _is_coroutine_or_asyncgen, which is what catches sync tests that happen to request async fixtures - exactly the gap #796 surfaced. Worth keeping the AUTO branch as-is even though it adds a per-fixture check.
2. The negative-case regression test test_parametrized_loop_policy_does_not_parametrize_sync_tests is paired with test_parametrized_loop_policy_parametrizes_sync_tests_with_async_fixtures (positive case). Good coverage pattern.

CI green across the full matrix (Py 3.10-3.14 + Windows + pytest main). Lint + mypy + pyright also clean per PR body.

Not a maintainer, leaving this as a non-blocking review.

[tjkuson]

I think this changes pytest's internals and breaks valid usage. For example, on main, this passes.

$ cat >mre.py <<'# EOF'
import asyncio
import pytest


@pytest.fixture(params=[asyncio.DefaultEventLoopPolicy(), asyncio.DefaultEventLoopPolicy()])
def policy(request):
    return request.param


@pytest.fixture
def event_loop_policy(policy):
    return policy


@pytest.mark.asyncio
async def test_async():
    pass


async def test_sync():
    pass
# EOF

$ pytest mre.py
==================================================== test session starts ====================================================
platform darwin -- Python 3.13.0, pytest-9.0.3, pluggy-1.6.0
rootdir: /Users/tjkuson/workspace/pytest-asyncio
configfile: pyproject.toml
plugins: asyncio-1.4.0a3.dev24
asyncio: mode=Mode.AUTO, debug=False, asyncio_default_fixture_loop_scope=function, asyncio_default_test_loop_scope=function
collected 2 items

mre.py EE                                                                                                             [100%]

========================================================== ERRORS ===========================================================
_______________________________________________ ERROR at setup of test_async ________________________________________________
The requested fixture has no parameter defined for test:
    mre.py::test_async

Requested fixture 'policy' defined in:
mre.py:6

Requested here:
.venv/lib/python3.13/site-packages/_pytest/fixtures.py:627
________________________________________________ ERROR at setup of test_sync ________________________________________________
The requested fixture has no parameter defined for test:
    mre.py::test_sync

Requested fixture 'policy' defined in:
mre.py:6

Requested here:
.venv/lib/python3.13/site-packages/_pytest/fixtures.py:627
===================================================== 2 errors in 0.02s =====================================================

[golikovichev]

Good catch with the MRE. My read was too superficial - I focused on the autouse change and the regression test pair, but missed that _add_fixture_to_metafunc injecting event_loop_policy breaks valid fixture chains where event_loop_policy depends on another parametrized fixture (like your policy). The patch shifts the parametrization origin out from under pytest's resolver.

Leaving this to the PR author and maintainers.

[golikovichev]

Re-reviewed after 8305b3a. The new _add_fixture_to_metafunc walks the closure via fixturemanager.getfixtureclosure() instead of attaching just the named fixture, so parametrize chains like event_loop_policy(policy) from @tjkuson's MRE are now preserved end to end.

The new test test_parametrized_loop_policy_can_depend_on_parametrized_fixture mirrors the MRE shape directly (parametrized policy fixture, event_loop_policy(policy) depending on it, both async and sync tests), so the regression is pinned. The two surrounding sync-vs-async parametrization tests cover the adjacent cases I would have asked for, so I do not have anything to add.

Sorry again for missing this in my first read - your MRE made the failure mode obvious, and the fix landed cleanly.

gmail-precheck-done