internal API, returns an iterator with all responses matching
        the request.

def _responses(self, request):
        """
        internal API, returns an iterator with all responses matching
        the request.
        """
        request = self._before_record_request(request)
        for index, (stored_request, response) in enumerate(self.data):
            if requests_match(request, stored_request, self._match_on):
                yield index, response