// UserController.java
@RestController
public class UserController {

    @Autowired
    private UserService userService;

    @GetMapping("/users/{id}")
    public User findUser(@PathVariable Long id) {
        return userService.findById(id);
    }
}

// UserService.java
@Service
public class UserService {

    @Autowired
    private UserRepo userRepo;

    public User findById(Long id) {
        return userRepo.findById(id);
    }
}


// UserRepo.java
@Service
public class UserRepo {

    public User findById(Long id) {
        return User.builder()
                .id(id)
                .name("Mac")
                .build();
    }
}

// User.java
@Data
@Builder
public class User {

    private Long id;
    private String name;

}

@RunWith(SpringRunner.class)
@SpringBootTest
public class UserServiceTest {

    @InjectMocks
    private UserService userService;

    @Mock
    private UserRepo userRepo;

    @Test
    public void testFindById() {
        Mockito.when(userRepo.findById(Mockito.anyLong())).thenReturn(User.builder()
                .id(1L)
                .name("Mac")
                .build());

        User user = userService.findById(1L);

        Assert.assertEquals(1L, user.getId().longValue());
        Assert.assertEquals("Mac", user.getName());
        Mockito.verify(userRepo, Mockito.times(1)).findById(Mockito.any());
    }
}

@RunWith(SpringRunner.class)
@WebMvcTest(UserController.class)
public class UserControllerTest {

    @Autowired
    private MockMvc mockMvc;

    @MockBean
    private UserService userService;

    @Autowired
    private ObjectMapper objectMapper;

    @Test
    public void testFindUser() throws Exception {

        User user = User.builder()
                .id(1L)
                .name("Mac")
                .build();
        Mockito.when(userService.findById(Mockito.any())).thenReturn(user);

        mockMvc.perform(MockMvcRequestBuilders.get("/users/1"))
                .andExpect(MockMvcResultMatchers.status().isOk())
                .andExpect(MockMvcResultMatchers.content()
                        .json(objectMapper.writeValueAsString(user)));
    }
}