Ensures :attr:`subject` is a :class:`collections.Mapping` and contains *keys*, which must be an iterable.

def has_keys(self, keys):
        """
        Ensures :attr:`subject` is a :class:`collections.Mapping` and contains *keys*, which must be an iterable.
        """
        self.is_a(Mapping)
        self.contains_all_of(keys)
        return ChainInspector(self._subject)