}
func cancelledContext() (context.Context, context.CancelFunc) {
	ctx, cancel := context.WithCancel(context.Background())
	cancel()
	return ctx, cancel
}
func deadlinedContext() (context.Context, context.CancelFunc) {
	ctx, cancel := context.WithTimeout(context.Background(), time.Millisecond)
	for ctx.Err() != context.DeadlineExceeded {
		time.Sleep(501 * time.Microsecond)
	}