如何模拟entityManager以对服务进行单元测试

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.mockito.Mock;
import org.mockito.MockitoAnnotations;

import javax.persistence.EntityManager;
import javax.persistence.Query;

import static org.mockito.Mockito.*;

public class MyServiceTest {

    @Mock
    private EntityManager entityManager;

    @Mock
    private Query query;

    private MyService myService;

    @BeforeEach
    public void setUp() {
        MockitoAnnotations.openMocks(this);
        when(entityManager.createQuery(anyString())).thenReturn(query);
        myService = new MyService(entityManager);
    }

    @Test
    public void testFindUserById() {
        // 模拟 Query 的结果
        when(query.getSingleResult()).thenReturn(new User(1L, "John Doe"));

        // 调用被测试的方法
        User user = myService.findUserById(1L);

        // 验证结果
        assertEquals(1L, user.getId());
        assertEquals("John Doe", user.getName());

        // 验证 EntityManager 和 Query 是否被正确调用
        verify(entityManager).createQuery("SELECT u FROM User u WHERE u.id = :id");
        verify(query).setParameter("id", 1L);
        verify(query).getSingleResult();
    }
}