// we want to make sure that Service will not leak the Activity
    // because of the registered the anonymous callback
    public void test () throws InterruptedException {
        Service service = new Service();
        Activity activity = new Activity(service);
        activity.onStart();

        // store a PhantomReference to watch the lifecycle of listener
        ReferenceQueue<Activity.Listener> referenceQueue = new ReferenceQueue<Activity.Listener>();
        PhantomReference<Activity.Listener> reference = new PhantomReference<Activity.Listener>(service.listener, referenceQueue); // no need to store this reference since it's a root object (in stack memory)

        activity.onStop();
//        reference = null; // uncomment to demonstrate why it's important to keep a strong reference to the PhantomReference
        activity = null; // at this point we removed the strong reference to our Activity,
        // service should not leak the Activity & Activity should be GC'd

        // trigger the collection of PhantomReference
        Runtime.getRuntime().gc();

        Reference<?> ref = referenceQueue.remove(TimeUnit.SECONDS.toMillis(10));
        assertNotNull(ref);
        ref.clear();
    }