'Assert the parser fails with the expected message.  Caller
must ensure that self.parser is an InterceptingOptionParser.'

def assertParseFail(self, cmdline_args, expected_output):

    try:
        self.parser.parse_args(cmdline_args)
    except InterceptedError as err:
        self.assertEqual(err.error_message, expected_output)
    else:
        self.assertFalse('expected    parse    failure')
