使用JUnit和Mockito测试：解决返回类型错误与Null问题

问题背景 #

实现了PatientServicesImpl类，其findByPatient方法依赖JwtServices解析JWT数据，再调用外部接口查询患者信息。相关核心代码如下：

PatientServicesImpl核心代码 #

@Autowired
private JwtServices jwtServices;

@Override
public Map<String, Object> findByPatient(String identificationNumber, String birthdate, Boolean allowPatientData)  {
    Map<String, String> jwtData = jwtServices.getDecoderJwt();

    Map<String, String> dataPatient =  new HashMap<>();
    dataPatient.put("identificationNumber", identificationNumber);
    dataPatient.put("birthdate",birthdate);
    dataPatient.put("allowPatientData",allowPatientData.toString());
    dataPatient.put("appointmentId",jwtData.get("sub"));

    return this.apiFaroConfig.findPatient(dataPatient);
}

JwtServices核心代码 #

@Autowired
private JWTDecoder jwtDecoder;

public Map<String, String> getDecoderJwt(){
    Map<String, String> jwtData = new HashMap<>();

    Payload payloadHeaderAuthorization = jwtDecoder.getPayloadAuthorization();

    jwtData.put("iss", payloadHeaderAuthorization.getIss());
    jwtData.put("sub",  payloadHeaderAuthorization.getSub());

    return jwtData;
}

编写测试代码后运行抛出错误：

org.mockito.exceptions.misusing.WrongTypeOfReturnValue: 
HashMap cannot be returned by getSub()
getSub() should return String

错误原因 #

1. Stub逻辑冲突：你同时尝试mockjwtServices.getDecoderJwt()的返回值，又保留了jwtDecoder和payload的mock对象。由于jwtServices是被@InjectMocks注入的真实对象，执行时会调用其真实逻辑，此时payload.getSub()未被指定返回值，Mockito内部错误地将你设置的jwtData（HashMap）关联到该方法，导致类型不匹配。
2. 测试逻辑错误：直接stub了要测试的patientServices.findByPatient()方法，完全跳过了目标方法的真实执行逻辑；最后调用的是外部接口方法而非目标测试方法，失去了测试意义。

修正后的测试代码 #

方案一：直接Mock JwtServices（推荐，专注测试PatientServicesImpl逻辑） #

该方案将JwtServices视为外部依赖直接mock，无需关注其内部实现，让测试聚焦于目标类的业务逻辑：

@ExtendWith(MockitoExtension.class)
class PatientServicesImplTest {

    @Mock
    private FaroApiRest apiFaroRest;

    @Mock // 直接mock JwtServices，隔离内部实现
    private JwtServices jwtServices;

    @InjectMocks
    private PatientServicesImpl patientServices;

    private Map<String, String> expectedDataPatient;
    private Map<String, Object> mockResponse;
    private Map<String, String> mockJwtData;

    @BeforeEach
    void setUp() {
        // 初始化mock JWT数据
        mockJwtData = new HashMap<>();
        mockJwtData.put("sub", "123456");

        // 构造预期传给外部接口的参数
        expectedDataPatient = new HashMap<>();
        expectedDataPatient.put("identificationNumber", "XXXX");
        expectedDataPatient.put("birthdate", "XXXX");
        expectedDataPatient.put("allowPatientData", "true");
        expectedDataPatient.put("appointmentId", "123456");

        // 初始化外部接口的mock返回值
        mockResponse = new HashMap<>();
        mockResponse.put("datosPersonales", "XXX");
        mockResponse.put("anamnesis", "XXX");
        mockResponse.put("gdpr", "XXX");
    }

    @Test
    void findByPatient_shouldReturnPatientData() {
        // 1. Stub依赖方法
        when(jwtServices.getDecoderJwt()).thenReturn(mockJwtData);
        when(apiFaroRest.findPatient(expectedDataPatient)).thenReturn(mockResponse);

        // 2. 调用要测试的方法
        Map<String, Object> actualResponse = patientServices.findByPatient("XXXX", "XXXX", true);

        // 3. 验证结果与依赖调用
        assertNotNull(actualResponse);
        assertTrue(actualResponse.containsKey("datosPersonales"));
        assertEquals(mockResponse, actualResponse);
        verify(apiFaroRest).findPatient(expectedDataPatient);
        verify(jwtServices).getDecoderJwt();
    }
}

方案二：完整Mock JwtServices的依赖（适合验证JwtServices内部逻辑场景） #

如果需要验证JwtServices的内部调用链，可以保留真实的JwtServices，并完整mock其依赖：

@ExtendWith(MockitoExtension.class)
class PatientServicesImplTest {

    @Mock
    private FaroApiRest apiFaroRest;

    @InjectMocks
    private JwtServices jwtServices; // 使用真实JwtServices，mock其依赖

    @Mock
    private JWTDecoder jwtDecoder;

    @Mock
    private Payload payload;

    @InjectMocks
    private PatientServicesImpl patientServices;

    private Map<String, String> expectedDataPatient;
    private Map<String, Object> mockResponse;

    @BeforeEach
    void setUp() {
        // Stub Payload的返回值，确保类型正确
        when(payload.getIss()).thenReturn("560");
        when(payload.getSub()).thenReturn("123456");

        // Stub JWTDecoder返回mock的Payload
        when(jwtDecoder.getPayloadAuthorization()).thenReturn(payload);

        // 构造预期传给外部接口的参数
        expectedDataPatient = new HashMap<>();
        expectedDataPatient.put("identificationNumber", "XXXX");
        expectedDataPatient.put("birthdate", "XXXX");
        expectedDataPatient.put("allowPatientData", "true");
        expectedDataPatient.put("appointmentId", "123456");

        // 初始化外部接口的mock返回值
        mockResponse = new HashMap<>();
        mockResponse.put("datosPersonales", "XXX");
        mockResponse.put("anamnesis", "XXX");
        mockResponse.put("gdpr", "XXX");
    }

    @Test
    void findByPatient_shouldReturnPatientData() {
        // Stub外部接口返回值
        when(apiFaroRest.findPatient(expectedDataPatient)).thenReturn(mockResponse);

        // 调用测试方法
        Map<String, Object> actualResponse = patientServices.findByPatient("XXXX", "XXXX", true);

        // 验证结果与依赖调用链
        assertNotNull(actualResponse);
        assertEquals(mockResponse, actualResponse);
        verify(jwtDecoder).getPayloadAuthorization();
        verify(payload).getSub();
        verify(apiFaroRest).findPatient(expectedDataPatient);
    }
}

关键修正点 #

• 明确测试边界：测试PatientServicesImpl时，优先将JwtServices视为外部依赖mock，避免被其内部实现干扰。
• 移除错误Stub：不要stub目标测试方法，直接调用并验证其行为和返回值。
• 正确Stub依赖：若使用真实依赖类，必须完整Stub其所有依赖方法的返回值，确保类型匹配。

内容的提问来源于stack exchange，提问作者Morante