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POTesting warnings with doctest
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copied!<p>I'd like to use <a href="http://docs.python.org/library/doctest.html" rel="noreferrer">doctests</a> to test the presence of certain warnings. For example, suppose I have the following module:</p> <pre><code>from warnings import warn class Foo(object): """ Instantiating Foo always gives a warning: >>> foo = Foo() testdocs.py:14: UserWarning: Boo! warn("Boo!", UserWarning) >>> """ def __init__(self): warn("Boo!", UserWarning) </code></pre> <p>If I run <code>python -m doctest testdocs.py</code> to run the doctest in my class and make sure that the warning is printed, I get:</p> <pre><code>testdocs.py:14: UserWarning: Boo! warn("Boo!", UserWarning) ********************************************************************** File "testdocs.py", line 7, in testdocs.Foo Failed example: foo = Foo() Expected: testdocs.py:14: UserWarning: Boo! warn("Boo!", UserWarning) Got nothing ********************************************************************** 1 items had failures: 1 of 1 in testdocs.Foo ***Test Failed*** 1 failures. </code></pre> <p>It looks like the warning is getting printed but not captured or noticed by doctest. I'm guessing that this is because warnings are printed to <code>sys.stderr</code> instead of <code>sys.stdout</code>. But this happens even when I say <code>sys.stderr = sys.stdout</code> at the end of my module.</p> <p>So is there any way to use doctests to test for warnings? I can find no mention of this one way or the other in the documentation or in my Google searching.</p>

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