pytest warnings due to deprecation of pytest.warns(None)

Pytest issues warnings about using pytest.warns(None) context manager, where the None part is now being deprecated.

For example, >>> pytest ./sklearn/tests/test_naive_bayes.py results in 79 passed, 4 warnings. After commenting out --disable-pytest-warnings key in [tool:pytest] section of setup.cfg, I could see that some of the warnings are:

PytestRemovedIn8Warning: Passing None has been deprecated. See https://docs.pytest.org/en/latest/how-to/capture-warnings.html#additional-use-cases-of-warnings-in-tests for alternatives in common use cases.

Apparently, pytest.warns(None) is deprecated for being widely misunderstood. I think that while sklearn’s tests do not suffer from this misunderstanding, they might be affected in the future if and when pytest raises an error instead of a deprecation warning. (I couldn’t figure out if this is planned for pytest’s future releases, but in any case, avoiding the deprecation and reducing the warnings count won’t harm.)

I found this message , which is relevant to how pytest.warns(None) is used in scikit-learn tests, and how this could be changed. I opened this issue to share this information and quote the message, as it may save someone time in the future.

The tests were of the form:

with pytest.warns(None) as record:
    <do some stuff>
    <check record for warnings, and possibly raise an error>

The tests were not assuming that the pytest context code would raise an error if a warning occurred. Instead, these tests were doing their own error checking based on record. So they were really using pytest.warns(None) exactly like warnings.catch_warnings(record=True). (There is a pull request to make the change to catch_warnings.)

[cmarmo]

Reopening as some tests still need to be modified.

[danifernandes-hub]

@adamgonzo I’m working on the utils folder. However, feel free to work on that file