@Override
  public void sendHeartbeatInvokeMessage(int currentId) {
    var nextInstance = this.findNextInstance(currentId);
    var heartbeatInvokeMessage = new Message(MessageType.HEARTBEAT_INVOKE, "");
    nextInstance.onMessage(heartbeatInvokeMessage);
  }
@Test
  void testSendHeartbeatInvokeMessage() {
    try {
      var instance1 = new BullyInstance(null, 1, 1);
      var instance2 = new BullyInstance(null, 1, 2);
      var instance3 = new BullyInstance(null, 1, 3);
      Map<Integer, Instance> instanceMap = Map.of(1, instance1, 2, instance2, 3, instance3);
      var messageManager = new BullyMessageManager(instanceMap);
      messageManager.sendHeartbeatInvokeMessage(2);
      var message = new Message(MessageType.HEARTBEAT_INVOKE, "");
      var instanceClass = AbstractInstance.class;
      var messageQueueField = instanceClass.getDeclaredField("messageQueue");
      messageQueueField.setAccessible(true);
      var messageSent = ((Queue<Message>) messageQueueField.get(instance3)).poll();
      assertEquals(messageSent.getType(), message.getType());
      assertEquals(messageSent.getContent(), message.getContent());
    } catch (NoSuchFieldException | IllegalAccessException e) {
      fail("Error to access private field.");
    }
  }