if err != nil {
		t.Fatal(err)
	}
	return dir, func() { os.RemoveAll(dir) }
}

const (
	quiescent            = 10 * time.Millisecond
	probablyStillBlocked = 10 * time.Second
)

func mustBlock(t *testing.T, desc string, f func()) (wait func(*testing.T)) {
	t.Helper()

	done := make(chan struct{})
	go func() {
		f()
		close(done)
	}()

	timer := time.NewTimer(quiescent)
	defer timer.Stop()