### Question:
UserServiceImpl extends ServiceImpl<UserMapper, UserDO> implements UserService { @Override public boolean checkUserExistById(Long id) { int rows = this.baseMapper.selectCountById(id); return rows > 0; }  @Transactional @Override UserDO createUser(RegisterDTO dto); @Transactional @Override UserDO updateUserInfo(UpdateInfoDTO dto); @Override UserDO changeUserPassword(ChangePasswordDTO dto); @Override List<GroupDO> getUserGroups(Long userId); @Override List<Map<String, List<Map<String, String>>>> getStructualUserPermissions(Long userId); @Override List<PermissionDO> getUserPermissions(Long userId); @Override UserDO getUserByUsername(String username); @Override boolean checkUserExistByUsername(String username); @Override boolean checkUserExistByEmail(String email); @Override boolean checkUserExistById(Long id); @Override IPage<UserDO> getUserPageByGroupId(Page pager, Long groupId);  }### Answer:
@Test public void checkUserExistById() { boolean b = userService.checkUserExistById(100L); assertFalse(b); }
@Test public void checkUserExistById1() { UserDO user = LocalUser.getLocalUser(); boolean b = userService.checkUserExistById(user.getId()); assertTrue(b); }