select {
	case <-idle:
		t.Errorf("NewQueue(1) is marked idle while processing work.")
	default:
	}

	close(unblock)
	<-idle // Should be closed as soon as the Add callback returns.
}

func TestQueueBacklog(t *testing.T) {
	const (
		maxActive = 2
		totalWork = 3 * maxActive
	)

	q := NewQueue(maxActive)
	t.Logf("q = NewQueue(%d)", maxActive)

	var wg sync.WaitGroup
	wg.Add(totalWork)