Add unit test to the modules: 
dubbo-registry/dubbo-registry-multicast
   dubbo-registry/dubbo-registry-redis
  dubbo-registry/dubbo-registry-zookeeper 
* {@link com.alibaba.dubbo.registry.multicast.MulticastRegistry#subscribe(URL url, com.alibaba.dubbo.registry.NotifyListener)}
     * .
     */
    @Test
    public void testSubscribe() {
        
        final AtomicReference<URL> args = new AtomicReference<URL>();
        registry.subscribe(consumerUrl, new NotifyListener() {
            @Override
            public void notify(List<URL> urls) {
                
                args.set(urls.get(0));
            }
        });
        assertEquals(serviceUrl.toFullString(), args.get().toFullString());
        Map<URL, Set<NotifyListener>> arg = registry.getSubscribed();
        assertEquals(consumerUrl, arg.keySet().iterator().next());
    }
    @Test
    public void testDefaultPort() {
        MulticastRegistry multicastRegistry = new MulticastRegistry(URL.valueOf("multicast://224.5.6.7"));
        try {
            MulticastSocket multicastSocket = multicastRegistry.getMutilcastSocket();
            Assert.assertEquals(1234, multicastSocket.getLocalPort());
        } finally {
            multicastRegistry.destroy();
        }
    }
}