// exit the program.
func ResetForTesting(usage func()) {
	CommandLine = NewFlagSet(os.Args[0], ContinueOnError)
	CommandLine.SetOutput(io.Discard)
	CommandLine.Usage = commandLineUsage
	Usage = usage

	// Note: This is not CommandLine.Usage = Usage,
	// because we want any eventual call to use any updated value of Usage,
	// not the value it has when this line is run.
	CommandLine.Usage = commandLineUsage
}

func commandLineUsage() {
	Usage()
}

// NewFlagSet returns a new, empty flag set with the specified name and
// error handling property. If the name is not empty, it will be printed