TopicManagerImpl implements TopicManager { @Override public Map<String, Collection<Session>> getSessionsByTopic() { return map; }  @Override Map<String, Collection<Session>> getSessionsByTopic(); @Override int registerTopicSession(String topic, Session session); @Override int unregisterTopicSession(String topic, Session session); @Override Collection<String> removeSessionsToTopic(Collection<Session> sessions); @Override Collection<String> removeSessionToTopics(Session session); @Override Collection<Session> getSessionsForTopic(String topic); @Override int getNumberSubscribers(String topic);  }
@Test public void getSessionsByTopicTest() { System.out.println("getSessionsByTopic"); Map result = instance.getSessionsByTopic(); assertThat(result).isInstanceOf(Map.class); }