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pythonunit-testingwarningsnose

Check that a function raises a warning with nose tests

I'm writing unit tests using nose, and I'd like to check whether a function raises a warning (the function uses warnings.warn). Is this something that can easily be done?

Solution 
  • def your_code():
    # ...
    warnings.warn("deprecated", DeprecationWarning)
    # ...

def your_test():
    with warnings.catch_warnings(record=True) as w:
        your_code()
        assert len(w) > 1

    Instead of just checking the lenght, you can check it in-depth, of course:

    assert str(w.args[0]) == "deprecated"

    In python 2.7 or later, you can do this with the last check as:

    assert str(w[0].message[0]) == "deprecated"