找不到 jUnit 测试返回 NullPointerException 的原因答案

【问题标题】：Cannot find why jUnit test return NullPointerException找不到 jUnit 测试返回 NullPointerException 的原因
【发布时间】：2017-12-17 08:37:16
【问题描述】：

我有一个简单的 Spring boot Rest 应用程序，它从数据库返回用户列表。应用程序按预期工作，但测试场景失败并出现错误。经过长时间的谷歌搜索无法弄清楚为什么？似乎测试类无法访问 userRepository，而不是调用 userRepository.getAllUsers，而是调用 AppController.getAllUsers。

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.NullPointerException
……………………………
Caused by: java.lang.NullPointerException
    at com.loan.demo.controller.AppController.getAllUsers(AppController.java:43)
 …………………………………………..

这些是我的课程： LoanAppApplication

@SpringBootApplication
public class LoanAppApplication {
public static void main(String[] args) {
    SpringApplication.run(LoanAppApplication.class, args);
}
}

类 User.java

@Entity
@Table(name="USERTABLE")
public class User {
private int id;
@NotNull
private String firstName;
@NotNull
private String lastName;
@NotNull
private String persID;
private int blocked;
private Set<Loan> loans;

public User() {
}
public User(String firstName, String lastName, String persID) {
    this.firstName = firstName;
    this.lastName = lastName;
    this.persID = persID;
}

用户存储库：

@Repository
public interface UserRepository extends JpaRepository<User, Integer>{
    public User findById(int Id);
    public User findByPersID(String userId);
}

和休息控制器：

@RestController
public class AppController {

    @Autowired
    UserRepository userRepository;

    @GetMapping("/doit")
    public String doIt() {
        return "Do It";
    }

    //list all users
    @GetMapping("/users")
    public List<User> getAllUsers() {
        return userRepository.findAll(); // this is line 43 from debuging error log
    }
}

和测试类：

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = {LoanAppApplication.class})
public class LoanAppApplicationTests {

    private MockMvc mockMvc;

    @InjectMocks
    private AppController appController;

    @Before
    public void addData() {
        mockMvc = MockMvcBuilders.standaloneSetup(appController)
                .build();
    }
    //First test scenario that return only string works perfectly
    @Test
    public void testData() throws Exception {
        mockMvc.perform(get("/doit")
                )
        .andExpect(status().isOk())
        .andExpect(content().string("Do It"));
    }
    //but second that should return empty json string fails with exception
    @Test
    public void testGet() throws Exception {
        mockMvc.perform(get("/users")
                )
        .andExpect(status().isOk())
        .andExpect(content().string("Do It")); //this test should fail but not return exception
    }
}

【问题讨论】：

标签： java unit-testing spring-boot-test

【解决方案1】：

你需要模拟你的 userRepository

@Mock
UserRepository userRepository;

所以在@Mock 之后你需要在@Before 中初始化Mock，添加这个：

MockitoAnnotations.initMocks(this);

然后在代码中设置你想获得什么用户

User user = new User();
when(userRepository.getUsers()).thenReturn(Collections.singletonList(user));

然后检查

verify(userRepository, times(1)).getUsers();
verifyNoMoreInteractions(userRepository);

这是因为您的应用程序上下文不工作

【讨论】：