1.1.0: Session fixture with `asyncio_default_fixture_loop_scope=function` yields `You tried to access the function scoped fixture _function_scoped_runner with a session scoped request object`

[mgorny]

Hit this in the wild while trying to run fakeredis's test suite.

Trivial reproducer:

import pytest_asyncio


@pytest_asyncio.fixture(scope="session")
def foo():
    pass


def test_foo(foo):
    pass

$ pytest -o asyncio_default_fixture_loop_scope=function test_foo.py -vv
========================================================= test session starts =========================================================
platform linux -- Python 3.13.5, pytest-8.4.1, pluggy-1.6.0 -- /tmp/fakeredis-py/.venv/bin/python3
cachedir: .pytest_cache
hypothesis profile 'default'
rootdir: /tmp
plugins: asyncio-1.1.0, hypothesis-6.136.6
asyncio: mode=Mode.STRICT, debug=False, asyncio_default_fixture_loop_scope=function, asyncio_default_test_loop_scope=function
collected 1 item                                                                                                                      

test_foo.py::test_foo ERROR                                                                                                     [100%]

=============================================================== ERRORS ================================================================
_____________________________________________________ ERROR at setup of test_foo ______________________________________________________
ScopeMismatch: You tried to access the function scoped fixture _function_scoped_runner with a session scoped request object. Requesting fixture stack:
test_foo.py:4:  def foo()
Requested fixture:
pytest-asyncio/pytest_asyncio/plugin.py:774:  def _scoped_runner(event_loop_policy, request: 'FixtureRequest') -> 'Iterator[Runner]'
======================================================= short test summary info =======================================================
ERROR test_foo.py::test_foo - Failed: ScopeMismatch: You tried to access the function scoped fixture _function_scoped_runner with a session scoped request object. Requesting fixture stack:
test_foo.py:4:  def foo()
Requested fixture:
pytest-asyncio/pytest_asyncio/plugin.py:774:  def _scoped_runner(event_loop_policy, request: 'FixtureRequest') -> 'Iterator[Runner]'
========================================================== 1 error in 0.12s ===========================================================

Reproduced on 92962d1.

[tjkuson]

I think the issue here is that the invocation scope is set to "session" (such that fixture called once per session), but the loop scope is set to "function" via the config (meaning the loop is reset once per function). The loop scope can't be narrower than the invocation scope, hence the error. Setting loop_scope="session" resolved the issue for me.

By the way, I was able to reproduce the issue using an async test and fixture (the example you gave uses a sync test and fixture, not sure if that's what you intended).

import pytest
import pytest_asyncio


@pytest_asyncio.fixture(scope="session")
async def foo():
    pass


@pytest.mark.asyncio
async def test_foo(foo):
    pass

[mgorny]

I'm sorry but I'm only a third party here — it looked like a regression in pytest-asyncio (it worked with the earlier versions), so I've reduced what fakeredis was doing and reported it here. Should I pass it on to fakeredis that it's not valid?

[tjkuson]

If my bisection was correct, this was introduced in 8b8e6e9. I'm not a maintainer, so can't say if this was intended.

Should I pass it on to fakeredis that it's not valid?

With the caveat that I'm not familiar with fakeredis, if your reproducer reflects what they are doing, it seems invalid. They shouldn't be using pytest_asyncio decorators on synchronous tests. If the test is supposed to be asynchronous, the loop scope can't be narrower than the invocation scope.