module 'pytest_cases' has no attribute 'CasesCollectionWarning' when running with xdist enabled

[lilo-d]

Hi,

started integrating pytest_cases in our unit testing suite (already did before in our integration testing suite), but I'm facing an issue at collection when running with xdist:

pytest -c ../pytest.ini -n 1 --rootdir=.

[Running Unit Tests]
=========================================================================================== test session starts ============================================================================================
platform darwin -- Python 3.8.12, pytest-6.1.2, py-1.10.0, pluggy-0.13.1
Test order randomisation NOT enabled. Enable with --random-order or --random-order-bucket=<bucket_type>
rootdir: /Users/lievenvanacker/Deliverect/backend/Tests/unit, configfile: ../pytest.ini
plugins: freezegun-0.4.2, redis-2.0.0, random-order-1.0.4, celery-4.4.7, xdist-2.3.0, anyio-3.4.0, mock-3.3.1, cov-2.10.1, asyncio-0.14.0, cases-3.6.8, mongodb-2.2.0, forked-1.3.0
gw0 ok!!!!!!!!!!!!!!!!!!!! <ExceptionInfo AttributeError("module 'pytest_cases' has no attribute 'CasesCollectionWarning'") tblen=2>
gw0 [4764]
INTERNALERROR> Traceback (most recent call last):
INTERNALERROR>   File "/Users/lievenvanacker/Deliverect/backend/venv/lib/python3.8/site-packages/xdist/workermanage.py", line 367, in process_from_remote
INTERNALERROR>     warning_message = unserialize_warning_message(
INTERNALERROR>   File "/Users/lievenvanacker/Deliverect/backend/venv/lib/python3.8/site-packages/xdist/workermanage.py", line 398, in unserialize_warning_message
INTERNALERROR>     cls = getattr(mod, data["message_class_name"])
INTERNALERROR> AttributeError: module 'pytest_cases' has no attribute 'CasesCollectionWarning'
[gw0] node down: <ExceptionInfo AttributeError("module 'pytest_cases' has no attribute 'CasesCollectionWarning'") tblen=2>
F
replacing crashed worker gw0
gw1 C     .INTERNALERROR> Traceback (most recent call last):
INTERNALERROR>   File "/Users/lievenvanacker/Deliverect/backend/venv/lib/python3.8/site-packages/_pytest/main.py", line 257, in wrap_session
INTERNALERROR>     session.exitstatus = doit(config, session) or 0
INTERNALERROR>   File "/Users/lievenvanacker/Deliverect/backend/venv/lib/python3.8/site-packages/_pytest/main.py", line 313, in _main
INTERNALERROR>     config.hook.pytest_runtestloop(session=session)
INTERNALERROR>   File "/Users/lievenvanacker/Deliverect/backend/venv/lib/python3.8/site-packages/pluggy/hooks.py", line 286, in __call__
INTERNALERROR>     return self._hookexec(self, self.get_hookimpls(), kwargs)
INTERNALERROR>   File "/Users/lievenvanacker/Deliverect/backend/venv/lib/python3.8/site-packages/pluggy/manager.py", line 93, in _hookexec
INTERNALERROR>     return self._inner_hookexec(hook, methods, kwargs)
INTERNALERROR>   File "/Users/lievenvanacker/Deliverect/backend/venv/lib/python3.8/site-packages/pluggy/manager.py", line 84, in <lambda>
INTERNALERROR>     self._inner_hookexec = lambda hook, methods, kwargs: hook.multicall(
INTERNALERROR>   File "/Users/lievenvanacker/Deliverect/backend/venv/lib/python3.8/site-packages/pluggy/callers.py", line 208, in _multicall
INTERNALERROR>     return outcome.get_result()
INTERNALERROR>   File "/Users/lievenvanacker/Deliverect/backend/venv/lib/python3.8/site-packages/pluggy/callers.py", line 80, in get_result
INTERNALERROR>     raise ex[1].with_traceback(ex[2])
INTERNALERROR>   File "/Users/lievenvanacker/Deliverect/backend/venv/lib/python3.8/site-packages/pluggy/callers.py", line 187, in _multicall
INTERNALERROR>     res = hook_impl.function(*args)
INTERNALERROR>   File "/Users/lievenvanacker/Deliverect/backend/venv/lib/python3.8/site-packages/xdist/dsession.py", line 112, in pytest_runtestloop
INTERNALERROR>     self.loop_once()
INTERNALERROR>   File "/Users/lievenvanacker/Deliverect/backend/venv/lib/python3.8/site-packages/xdist/dsession.py", line 135, in loop_once
INTERNALERROR>     call(**kwargs)
INTERNALERROR>   File "/Users/lievenvanacker/Deliverect/backend/venv/lib/python3.8/site-packages/xdist/dsession.py", line 278, in worker_runtest_protocol_complete
INTERNALERROR>     self.sched.mark_test_complete(node, item_index, duration)
INTERNALERROR>   File "/Users/lievenvanacker/Deliverect/backend/venv/lib/python3.8/site-packages/xdist/scheduler/load.py", line 151, in mark_test_complete
INTERNALERROR>     self.node2pending[node].remove(item_index)
INTERNALERROR> KeyError: <WorkerController gw0>
!!!!!!!!!!!!!!!!!!!! <ExceptionInfo AttributeError("module 'pytest_cases' has no attribute 'CasesCollectionWarning'") tblen=2>
INTERNALERROR> Traceback (most recent call last):
INTERNALERROR>   File "/Users/lievenvanacker/Deliverect/backend/venv/lib/python3.8/site-packages/xdist/workermanage.py", line 367, in process_from_remote
INTERNALERROR>     warning_message = unserialize_warning_message(
INTERNALERROR>   File "/Users/lievenvanacker/Deliverect/backend/venv/lib/python3.8/site-packages/xdist/workermanage.py", line 398, in unserialize_warning_message
INTERNALERROR>     cls = getattr(mod, data["message_class_name"])
INTERNALERROR> AttributeError: module 'pytest_cases' has no attribute 'CasesCollectionWarning'

Note that running without xdist works fine:

pytest -c ../pytest.ini --rootdir=.

Not sure if this is our setup or a general issue? I could help to further debug if needed.

Thanks, Lieven

[smarie]

It seems from the traceback that the issue comes from xdist in unserializing the warning message:

xdist/workermanage.py (unserialize_warning_message) seems to expect that the warning class is always a top-level attribute of the main package: cls = getattr(mod, data["message_class_name"])

I found a similar issue in pytest-xdist: pytest-dev/pytest-xdist#404
I asked them for guidance

[smarie]

I found the culprit:

python-pytest-cases/src/pytest_cases/case_parametrizer_new.py

Lines 682 to 686 in 8d11b7d

	class CasesCollectionWarning(UserWarning):
	"""
	Warning emitted when pytest cases is not able to collect a file or symbol in a module.
	"""
	__module__ = "pytest_cases"

The issue is that I set __module__ myself so that the warning message looks nice... However then the __init__ should contain the class for consistency.

[smarie]

@lilo-d please note that the CasesCollectionWarning means that there is at least one class containing cases, that is ignored in your tests because it contains __init__ or __new__. So, probably something to check on your side as well (even when the bug is fixed)