assertWarns(expected_warning, *args, **kwargs)¶
Fail unless a warning of class warnClass is triggered by the callable when invoked with specified positional and keyword arguments. If a different type of warning is triggered, it will not be handled: depending on the other warning filtering rules in effect, it might be silenced, printed out, or raised as an exception.
If called with the callable and arguments omitted, will return a context object used like this:
with self.assertWarns(SomeWarning): do_something()
An optional keyword argument ‘msg’ can be provided when assertWarns is used as a context object.
The context manager keeps a reference to the first matching warning as the ‘warning’ attribute; similarly, the ‘filename’ and ‘lineno’ attributes give you information about the line of Python code from which the warning was triggered. This allows you to inspect the warning after the assertion:
with self.assertWarns(SomeWarning) as cm: do_something() the_warning = cm.warning self.assertEqual(the_warning.some_attribute, 147)