### Question:
Ros { public long nextId() { return this.idCounter++; } Ros();  Ros(String hostname);  Ros(String hostname, int port);  Ros(String hostname, int port, JRosbridge.WebSocketType protocol); String getHostname(); int getPort(); JRosbridge.WebSocketType getProtocol(); String getURL(); long nextId(); void addRosHandler(RosHandler handler); boolean connect(); boolean disconnect(); boolean isConnected(); @OnOpen void onOpen(Session session); @OnClose void onClose(Session session); @OnError void onError(Session session, Throwable t); @OnMessage void onMessage(String message); boolean send(JsonObject jsonObject); void authenticate(String mac, String client, String dest,
			String rand, int t, String level, int end); void registerTopicCallback(String topic, TopicCallback cb); void deregisterTopicCallback(String topic, TopicCallback cb); void registerServiceCallback(String serviceCallId, ServiceCallback cb); void registerCallServiceCallback(String serviceName, CallServiceCallback cb); void deregisterCallServiceCallback(String serviceName); static final String DEFAULT_HOSTNAME; static final int DEFAULT_PORT; }### Answer:
@Test public void testNextID() { for (int i = 0; i < 20; i++) { assertEquals((long) i, r1.nextId()); assertEquals((long) i, r2.nextId()); assertEquals((long) i, r3.nextId()); assertEquals((long) i, r4.nextId()); } }