Ensures :attr:`subject` contains none of *elements*, which must be an iterable.

def contains_none_of(self, elements):
        """
        Ensures :attr:`subject` contains none of *elements*, which must be an iterable.
        """
        for element in elements:
            self._run(unittest_case.assertNotIn, (element, self._subject))
        return ChainInspector(self._subject)