### Question:
MulticastRegistry extends FailbackRegistry { @Override public void subscribe(URL url, NotifyListener listener) { super.subscribe(url, listener); subscribed(url, listener); } MulticastRegistry(URL url); @Override void doRegister(URL url); @Override void doUnregister(URL url); @Override void doSubscribe(URL url, NotifyListener listener); @Override void doUnsubscribe(URL url, NotifyListener listener); @Override boolean isAvailable(); @Override void destroy(); @Override void register(URL url); @Override void unregister(URL url); @Override void subscribe(URL url, NotifyListener listener); @Override void unsubscribe(URL url, NotifyListener listener); @Override List<URL> lookup(URL url); MulticastSocket getMulticastSocket(); Map<URL, Set<URL>> getReceived();  }### Answer:
@Test public void testSubscribe() { registry.subscribe(consumerUrl, new NotifyListener() { @Override public void notify(List<URL> urls) { assertEquals(serviceUrl.toFullString(), urls.get(0).toFullString()); Map<URL, Set<NotifyListener>> subscribed = registry.getSubscribed(); assertEquals(consumerUrl, subscribed.keySet().iterator().next()); } }); }