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"The test […] is not an async function" when asyncio marker is added via pytest_collection_modifyitems() #810
Description
This one I've noticed while testing IPython. The simplest reproducer is:
conftest.py:
import inspect
def pytest_collection_modifyitems(items):
for item in items:
if inspect.iscoroutinefunction(item.obj):
item.add_marker("asyncio")test_foo.py:
async def test_foo():
passWith pytest-asyncio 0.23.6, I'm getting:
========================================================= test session starts =========================================================
platform linux -- Python 3.11.8, pytest-8.1.1, pluggy-1.4.0
rootdir: /tmp/repro
plugins: asyncio-0.23.6
asyncio: mode=Mode.STRICT
collected 1 item
test_foo.py s [100%]
========================================================== warnings summary ===========================================================
test_foo.py::test_foo
test_foo.py:5: PytestWarning: The test <Function test_foo> is marked with '@pytest.mark.asyncio' but it is not an async function. Please remove the asyncio mark. If the test is not marked explicitly, check for global marks applied via 'pytestmark'.
async def test_foo():
test_foo.py::test_foo
/tmp/repro/.venv/lib/python3.11/site-packages/_pytest/python.py:184: PytestUnhandledCoroutineWarning: async def functions are not natively supported and have been skipped.
You need to install a suitable plugin for your async framework, for example:
- anyio
- pytest-asyncio
- pytest-tornasync
- pytest-trio
- pytest-twisted
warnings.warn(PytestUnhandledCoroutineWarning(msg.format(nodeid)))
-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
=================================================== 1 skipped, 2 warnings in 0.01s ====================================================With pytest-asyncio-0.21.1, the test is correctly run as marked.
Activity
mgorny commentedon Apr 16, 2024
Also affects PyZMQ.
seifertm commentedon May 26, 2025
Still reproducible in pytest-asyncio v1.0.0a1.
JiwaniZakir commentedon Mar 16, 2026
I think I see what's going on here. Going to put together a fix.
test: add regression test for issue pytest-dev#810
tjkuson commentedon May 8, 2026
As of the 1.4 alphas, I am not sure if there is a way for pytest-asyncio to support late markers safely. The plugin uses the presence of the
asynciomarker to determine what items to parametrize and how to parametrize them. By the timepytest_collection_modifyitemsis run, the items have been parametrized and pytest, from what I can tell, does not support late parametrization (at least, not without implementing a hack via its internals).Applying the markers via
pytest_pycollect_makeitembefore pytest-asyncio's collection-time conversion happens should work and would mean that items participate in parametrization as intended. Does that fix your use case?