fmt.Fprintln(os.Stderr, fmt.Sprintf(f, args...))
	os.Exit(1)
}

type GoCallback struct{}

func (p *GoCallback) Run() string {
	return "GoCallback.Run"
}

func testCall() {
	c := NewCaller()
	cb := NewCallback()

	c.SetCallback(cb)
	s := c.Call()
	if s != "Callback::run" {
		fatal("unexpected string from Call: %q", s)
	}
	c.DelCallback()
}

func testCallback() {
	c := NewCaller()

	// go test will hang forever.
	//
	// Avoid that by wrapping stderr, breaking the short circuit and
	// forcing cmd.Run to use another pipe and goroutine to pass
	// along stderr from adb.
	cmd.Stderr = struct{ io.Writer }{os.Stderr}
	err := cmd.Run()

	// Before we process err, flush any further output and get the exit code.
	exitCode, err2 := filter.Finish()

	if err != nil {