def assert_no_pending(self, target_rule=None):
        '''
        Raises a :class:`PendingRequestsLeftException` error if server has target rule
        non-resolved.

        When target_rule argument is ommitted raises if server has any pending
        expectations.

        Useful in ``tearDown()`` test method to verify that test had correct expectations

        :type target_rule: Rule
        :param target_rule: will raise if this rule is left pending

        :raises: :class:`PendingRequestsLeftException`
        '''
        if target_rule:
            if target_rule in self._rules:
                raise PendingRequestsLeftException()
        elif self._rules:
            raise PendingRequestsLeftException()
Raises a :class:`PendingRequestsLeftException` error if server has target rule
        non-resolved.

        When target_rule argument is ommitted raises if server has any pending
        expectations.

        Useful in ``tearDown()`` test method to verify that test had correct expectations

        :type target_rule: Rule
        :param target_rule: will raise if this rule is left pending

        :raises: :class:`PendingRequestsLeftException`