def raise_failure_exception(self, expect_or_allow='Allowed'):
        """Raises a ``MockExpectationError`` with a useful message.

        :raise: ``MockExpectationError``
        """

        raise MockExpectationError(
            "{} '{}' to be called {}on {!r} with {}, but was not. ({}:{})".format(
                expect_or_allow,
                self._method_name,
                self._call_counter.error_string(),
                self._target.obj,
                self._expected_argument_string(),
                self._caller.filename,
                self._caller.lineno,
            )
        )
Raises a ``MockExpectationError`` with a useful message.

        :raise: ``MockExpectationError``