### Question:
UserDao { public UserDO findById(Integer id) { return mongoTemplate.findOne(new Query(Criteria.where("_id").is(id)), UserDO.class); }  void insert(UserDO entity); void updateById(UserDO entity); void deleteById(Integer id); UserDO findById(Integer id); UserDO findByUsername(String username); List<UserDO> findAllById(List<Integer> ids);  }### Answer:
@Test public void testSelectById() { UserDO userDO = userDao.findById(1); System.out.println(userDO); }