SpringBoot单元测试中@SpyBean使用小结

@Service
public class UserService {
    @Autowired
    private UserRepository userRepository;

    public String getUserName(Long id) {
        User user = userRepository.findById(id).orElseThrow();
        return user.getName();
    }
}

@SpringBootTest
public class UserServiceTest {

    @Autowired
    private UserService userService;

    @SpyBean  // 对 UserRepository 进行 Spy，未 Mock 的方法仍然走真实逻辑
    private UserRepository userRepository;

    @Test
    public void testGetUserName() {
        // 准备测试数据
        User mockUser = new User(1L, "Alice");
        userRepository.save(mockUser);  // 真实调用 save()

        // 只 Mock findById()，让它返回自定义数据
        doReturn(Optional.of(new User(1L, "Mocked Alice")))
            .when(userRepository).findById(1L);

        // 调用测试方法
        String userName = userService.getUserName(1L);

        // 验证
        assertEquals("Mocked Alice", userName);

        // 其他方法仍然走真实逻辑
        User savedUser = userRepository.findById(2L).orElse(null);
        assertNull(savedUser);  // 因为没有存 ID=2 的用户
    }
}

// 让方法返回固定值
doReturn("Mocked Result").when(mySpyBean).someMethod();

// 带参数匹配
doReturn("Hello").when(mySpyBean).greet(anyString());

doAnswer(invocation -> {
    String arg = invocation.getArgument(0);
    return "Processed: " + arg;
}).when(mySpyBean).process(anyString());

doThrow(new RuntimeException("DB Error"))
    .when(mySpyBean).save(any());

// 默认会走真实方法，但也可以显式声明
doCallRealMethod().when(mySpyBean).someMethod();

// 验证 someMethod 被调用 1 次
verify(mySpyBean, times(1)).someMethod();