@Override
  public boolean sendHeartbeatMessage(int leaderId) {
    var leaderInstance = instanceMap.get(leaderId);
    return leaderInstance.isAlive();
  }
@Test
  void testSendHeartbeatMessage() {
    var instance1 = new BullyInstance(null, 1, 1);
    Map<Integer, Instance> instanceMap = Map.of(1, instance1);
    var messageManager = new BullyMessageManager(instanceMap);
    assertTrue(messageManager.sendHeartbeatMessage(1));
  }