Treating warnings as errors in pytest#

I was seeing this warning in a Django project when I thought I was correctly using timezone-aware dates everywhere:

RuntimeWarning: DateTimeField Shift.shift_start received a naive datetime (2022-04-01 00:00:00) while time zone support is active

Running pytest -Werror turns those warnings into errors that fail the tests.

Which means you can investigate them in the Python debugger by running:

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pytest -Werror --pdb -x

The --pdb starts the debugger at the warning (now error) and the -x stops the tests after the first failure.

In pytest.ini#

You can also set this in pytest.ini - useful if you want ALL warnings to be failures in both development and CI.

Add the following to the pytest.ini file:

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[pytest]
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# ...
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filterwarnings =
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    error

If you do this you may find there are warnings you cannot fix (because they are in dependency libraries). You can ignore those like this:

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[pytest]
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# ...
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filterwarnings =
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    error
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    ignore::arrow.factory.ArrowParseWarning

You need to figure out the full path to the warning. I used --pdb to figure this out.