Method assertWarns

Lib/unittest/case.py:823–852

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 effe

(self, expected_warning, *args, **kwargs)

            context = None

    def assertWarns(self, 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)
        """
        context = _AssertWarnsContext(expected_warning, self)
        return context.handle('assertWarns', args, kwargs)

    def _assertNotWarns(self, expected_warning, *args, **kwargs):
        """The opposite of assertWarns. Private due to low demand."""