Test if an boolean is False

def __assert_false(returned):
        '''
        Test if an boolean is False
        '''
        result = "Pass"
        if isinstance(returned, str):
            try:
                returned = bool(returned)
            except ValueError:
                raise
        try:
            assert (returned is False), "{0} not False".format(returned)
        except AssertionError as err:
            result = "Fail: " + six.text_type(err)
        return result