Add unit test to the modules: 
dubbo-registry/dubbo-registry-multicast
   dubbo-registry/dubbo-registry-redis
  dubbo-registry/dubbo-registry-zookeeper 
logger.warn("Clean expired provider " + url);
                        }
                        doUnregister(url);
                    }
                }
            }
        }
    }
    private boolean isExpired(URL url) {
        if (!url.getParameter(Constants.DYNAMIC_KEY, true)
                || url.getPort() <= 0
                || Constants.CONSUMER_PROTOCOL.equals(url.getProtocol())
                || Constants.ROUTE_PROTOCOL.equals(url.getProtocol())
                || Constants.OVERRIDE_PROTOCOL.equals(url.getProtocol())) {
            return false;
        }
        Socket socket = null;
        try {
            socket = new Socket(url.getHost(), url.getPort());
        } catch (Throwable e) {
            try {
                Thread.sleep(100);
            } catch (Throwable e2) {
            }
            Socket socket2 = null;
            try {
                socket2 = new Socket(url.getHost(), url.getPort());
            } catch (Throwable e2) {
                return true;
            } finally {