### Question:
MessengerServiceImpl implements MessengerService { @Override public void addMessenger(Messenger messenger) { em.persist(messenger); }  @Override List<Messenger> getAll(); @Override void addMessenger(Messenger messenger); @Override List<Messenger> getMessenger(String sendId, String receiveId); @Override int seenMessage(Messenger messenger); @Override List<Object> getInfo(String userId);  }### Answer:
@Test void addMessengerTest() { int size = initDataStore(); Messenger messenger = new Messenger("Ho","1234","1236"); Messengerserviceimpl.addMessenger(messenger); List<Messenger> messengers = Messengerserviceimpl.getAll(); int size2 = messengers.size(); assertEquals(size+1,size2); }