### Question:
MulticastRegistry extends FailbackRegistry { @Override public boolean isAvailable() { try { return multicastSocket != null; } catch (Throwable t) { return false; } } 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 testAvailability() { int port = NetUtils.getAvailablePort(); MulticastRegistry registry = new MulticastRegistry(URL.valueOf("multicast: assertTrue(registry.isAvailable()); }