add integration test for createuser method

src/main/java/com/cloudcomputing/todo/dto/UserDTO.java

src/main/java/com/cloudcomputing/todo/entity/User.java

src/main/java/com/cloudcomputing/todo/mapper/UserMapper.java

...va/com/cloudcomputing/todo/repository/UserRepository.java

...ain/java/com/cloudcomputing/todo/service/UserService.java

...java/com/cloudcomputing/todo/service/UserServiceTest.java