then:
        def e = thrown(CommandLineArgumentException)
        e.message == 'Unknown command-line option \'--unknown\'.'
    }

    def parseFailsWhenCommandLineContainsUnknownLongOptionWithSingleDashes() {
        when:
        parser.parse(['-unknown'])

        then:
        def e = thrown(CommandLineArgumentException)
        e.message == 'Unknown command-line option \'-u\'.'