Add unit test to the modules: 
dubbo-registry/dubbo-registry-multicast
   dubbo-registry/dubbo-registry-redis
  dubbo-registry/dubbo-registry-zookeeper 
if (socket2 != null) {
                    try {
                        socket2.close();
                    } catch (Throwable e2) {
                    }
                }
            }
        } finally {
            if (socket != null) {
                try {
                    socket.close();
                } catch (Throwable e) {
                }
            }
        }
        return false;
    }
    private void receive(String msg, InetSocketAddress remoteAddress) {
        if (logger.isInfoEnabled()) {
            logger.info("Receive multicast message: " + msg + " from " + remoteAddress);
        }
        if (msg.startsWith(Constants.REGISTER)) {
            URL url = URL.valueOf(msg.substring(Constants.REGISTER.length()).trim());
            registered(url);
        } else if (msg.startsWith(Constants.UNREGISTER)) {
            URL url = URL.valueOf(msg.substring(Constants.UNREGISTER.length()).trim());
            unregistered(url);
        } else if (msg.startsWith(Constants.SUBSCRIBE)) {
            URL url = URL.valueOf(msg.substring(Constants.SUBSCRIBE.length()).trim());
            Set<URL> urls = getRegistered();