Pytest hanging

[wonboyn]

Hi there,

We have a test suite of approximately 4000 items.

If we run pytest against the test directory it hangs at a certain test module every time (./testing/views/test_fred.py) . If we manually specify the all the test directories & put the directory with the test module that hangs first (eg pytest ./testing/views/test_fred.py ./testing/abc/test_abc.py ./testing/def/test_def.py ./testing/ghi/test_ghi.py ...) it works fine.

If we just run the test module that hangs on its own it also works fine.

I'd appreciate any guidance on how to get any additional logging/tracing information from pytest about what is happening & causing the test run to slow right down.

Our environment:

• python v3.6.9
• pytest v6.2.5
• pytest-cases v3.6.7

Thanks in advance.

Tim

[portyu9]

Hi @wonboyn

The fact that the module runs successfully by itself and also works when moved earlier in the suite strongly suggests an order-dependent resource/state problem, although the information in the post is not enough to identify which resource.

I would debug it in this order:

pytest -vv
pytest -vv --setup-show

Then run the hanging test together with progressively smaller subsets of the tests that precede it. That usually identifies the test which leaves behind the problematic state/resource.

For a hang, pytest's built-in faulthandler support is particularly useful. For example in pytest.ini:

[pytest]
faulthandler_timeout = 30

If execution is stuck for 30 seconds, pytest will dump Python thread stack traces, which can reveal a lock, network call, subprocess wait, etc.

Because the versions in the post are Python 3.6 / pytest 6.2.5, I would also reproduce on a supported Python version and current pytest before treating this as a pytest-core bug.

Please mark this answer as accepted if it helped, thank you.