pytest should integrate with warnings module

[pytestbot]

Originally reported by: Andreas Kloeckner (BitBucket: inducer, GitHub: inducer)

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Hi there,

I would like it if pytest could highlight tests that trigger Python warnings via the warnings module, print statistics on them, and, optionally, print all those warnings. When (especially deprecation) warnings are used to evolve interfaces, this allows catching all those early on as opposed to when they actually cause an error.

Thanks,
Andreas

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• Bitbucket: https://bitbucket.org/pytest-dev/pytest/issue/253

[RonnyPfannschmidt]

https://github.com/fschulze/pytest-warnings is a starting point that will be merged into core later on