Make sure you didn't emit any warnings while testing
Description
In general, your tests shouldn't produce warnings. This module causes any
warnings to be captured and stored. It automatically adds an extra test
that will run when your script ends to check that there were no warnings.
If there were any warnings, the test will give a "not ok" and diagnostics of
where, when and what the warning was, including a stack trace of what was
going on when the it occurred.
