code: @Test public void testSubscribe(){
    NotifyListener listener=mock(NotifyListener.class);
    zookeeperRegistry.subscribe(serviceUrl,listener);
    Map<URL,Set<NotifyListener>> subscribed=zookeeperRegistry.getSubscribed();
    assertThat(subscribed.size(),is(1));
    assertThat(subscribed.get(serviceUrl).size(),is(1));
    zookeeperRegistry.unsubscribe(serviceUrl,listener);
    subscribed=zookeeperRegistry.getSubscribed();
    assertThat(subscribed.size(),is(1));
    assertThat(subscribed.get(serviceUrl).size(),is(0));
  }
  