if n != len(buf) || err != nil || string(buf) != "O:hi\n" {
		t.Fatalf("ReadFull = %d, %v, %q", n, err, buf[:n])
	}
	go cancel()

	if err := c.Wait(); err == nil {
		t.Fatal("expected Wait failure")
	}
}

func TestContextCancel(t *testing.T) {
	if runtime.GOOS == "netbsd" && runtime.GOARCH == "arm64" {
		maySkipHelperCommand("cat")
		testenv.SkipFlaky(t, 42061)
	}

	// Using After(10ms) but waiting for 500ms to read the channel
	// should produce a time from start+10ms, not start+500ms.
	// Make sure it does.
	// To avoid flakes due to very long scheduling delays,
	// require 10 failures in a row before deciding something is wrong.
	for range 10 {
		start := Now()
		c := After(10 * Millisecond)
		Sleep(500 * Millisecond)
		dt := (<-c).Sub(start)
		if dt < 400*Millisecond {
			return
		}

//
// After a successful call to Start the [Cmd.Wait] method must be called in
// order to release associated system resources.
func (c *Cmd) Start() error {
	// Check for doubled Start calls before we defer failure cleanup. If the prior
	// call to Start succeeded, we don't want to spuriously close its pipes.
	if c.Process != nil {
		return errors.New("exec: already started")
	}

	started := false
	defer func() {