Add unit test to the modules: 
dubbo-registry/dubbo-registry-multicast
   dubbo-registry/dubbo-registry-redis
  dubbo-registry/dubbo-registry-zookeeper 
}
    }
    @Override
    protected void doUnsubscribe(URL url, NotifyListener listener) {
        if (!Constants.ANY_VALUE.equals(url.getServiceInterface())
                && url.getParameter(Constants.REGISTER_KEY, true)) {
            unregister(url);
        }
        broadcast(Constants.UNSUBSCRIBE + " " + url.toFullString());
    }
    @Override
    public boolean isAvailable() {
        try {
            return mutilcastSocket != null;
        } catch (Throwable t) {
            return false;
        }
    }
    @Override
    public void destroy() {
        super.destroy();
        try {
            if (cleanFuture != null) {
                cleanFuture.cancel(true);
            }
        } catch (Throwable t) {
            logger.warn(t.getMessage(), t);
        }
        try {
            mutilcastSocket.leaveGroup(mutilcastAddress);