선생님들 도와주세요~

package com.example.demo;

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.annotation.Rollback;

import javax.transaction.Transactional;
@SpringBootTest
@Transactional(rollbackOn = {Exception.class})
class Repository_CookerTest {

    @Autowired
    Service_Cooker Service_Cooker;

    @Autowired
    Repository_Cooker repositoryCooker;

    @Test
    @Rollback(value = false)
    void 테스트(){
        Cooker cooker=new Cooker();
        cooker.setId(123L);
        cooker.setExp(1);
        cooker.setName("123");
        cooker.setAge(23);
        Long id=Service_Cooker.save(cooker);

        Assertions.assertEquals(cooker,repositoryCooker.find_one(id));

    }

}

package com.example.demo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Repository;

import javax.persistence.EntityManager;

@Repository
public class Repository_Cooker {

    @Autowired
    private EntityManager entityManager;

    public void save(Cooker cooker){

        entityManager.persist(cooker);

    }

    public Cooker find_one(Long id){
        return entityManager.find(Cooker.class,id);
    }



}

package com.example.demo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class Service_Cooker {
    @Autowired
    Repository_Cooker repository_Cooker;

    public Long save(Cooker cooker){
       repository_Cooker.save(cooker);
       return cooker.getId();
    }
}

org.springframework.dao.InvalidDataAccessApiUsageException: detached entity passed to persist: com.example.demo.Cooker; nested exception is org.hibernate.PersistentObjectException: detached entity passed to persist: com.example.demo.Cooker

 insert into cooker (cooker_id, age, exp, name) values (null, 23, 1, '123');

안녕하세요 영한 선생님

덕분에 쑥쑥 자라나고 있는 코린이입니다.

질문은 아이디 없이

테스트를 돌리면 통과가 되는데요

아이디를 설정하고 돌리면 에러가 납니다.

왜 그런건지 어디가 잘못된 건지 알고싶어요 ~

도와주세요~