Assert that mapping.keys() == FIELDS.

        The programmer is not supposed to pass extra/less number of fields

def __assert_field_mapping(self, mapping):
        """Assert that mapping.keys() == FIELDS.

        The programmer is not supposed to pass extra/less number of fields
        """
        passed_keys = set(mapping.keys())
        class_fields = set(self.FIELDS)

        if passed_keys != class_fields:
            raise ValueError('\n'.join([
                "{0} got different fields from expected".format(
                    self.__class__),
                "  got     : {0}".format(list(sorted(passed_keys))),
                "  expected: {0}".format(list(sorted(class_fields)))]))