测试LocationService异常场景遇空指针，求无源码修改的解决方案

测试LocationServiceImpl的getLocationById方法异常场景时，当LocationRepository查询不到对应locationId时，预期抛出CustomException，但实际抛出了NullPointerException。已尝试通过when(locationRepository.findById(anyString())).thenReturn(Optional.empty())模拟数据，也将anyString替换为随机字符串，但问题未解决。调试发现异常出现在Location location = locationRepository.findById(locationId).orElseThrow代码块中，希望在不修改业务源码的前提下完成测试。

业务服务方法 #

@Slf4j
@Service
@AllArgsConstructor
public class LocationServiceImpl implements LocationService {

    private final LocationRepository locationRepository;

    public LocationMobieDTO getLocationById(HttpHeaders headers, String locationId) {
        credentialService.checkRegistered(headers);
        Location location = locationRepository.findById(locationId).orElseThrow(() -> {
            KafkaMessageDTO<String> messageDTO = KafkaMessageDTO.<String>builder().id(locationId).build();
            messageServiceString.sendMessage(
                KafkaTopics.TEST.topic,
                messageServiceString.prepareMsg(ResponseEnum.UNKNOWN_LOCATION, messageDTO)
            );
            return new CustomException(ResponseEnum.UNKNOWN_LOCATION);
        });
        return mapper.mapperLocationToDTO(location);
    }
}

测试用例 #

@ExtendWith(MockitoExtension.class)
public class LocationServiceTest {
    @InjectMocks
    private LocationServiceImpl locationService;

    @Mock
    private LocationRepository locationRepository;

    @Test
    void whenGetLocationById_thenReturnCustomException() {
        // Given
        when(locationRepository.findById(anyString())).thenReturn(Optional.empty());

        // When 
        CustomException exception = assertThrows(CustomException.class, () -> {
            locationService.getLocationById(headers, anyString());
        });

        // Then
        assertEquals(ResponseEnum.UNKNOWN_LOCATION, exception.getException());
    }
}

控制器代码 #

@GetMapping(value = "/{country_code}/{party_id}/{location_id}")
public Response<LocationMobieDTO> getLocationById(@RequestHeader HttpHeaders headers, @PathVariable("location_id") String locationId){
    
    return Response.<LocationMobieDTO>builder()
            .data(locationService.getLocationById(headers, locationId))
            .statusCode(ResponseEnum.SUCCESS.getStatusCode())
            .statusMessage(ResponseEnum.SUCCESS.getStatusMessage())
            .timestamp(Instant.now().toString()).build();
}

错误信息 #

org.opentest4j.AssertionFailedError: Unexpected exception type thrown ==] expected: [com.demo.myapi.exception.CustomException] but was: [java.lang.NullPointerException]
 at com.demo.myapi.location.service.LocationServiceTest.whenGetLocationById_thenReturnCustomException(LocationServiceTest.java:177)
 at java.base/java.util.ArrayList.forEach(ArrayList.java:1541)
 at java.base/java.util.ArrayList.forEach(ArrayList.java:1541)
Caused by: java.lang.NullPointerException
 at com.demo.myapi.location.service.LocationServiceImpl.lambda$0(LocationServiceImpl.java:95)
 at java.base/java.util.Optional.orElseThrow(Optional.java:408)
 at com.demo.myapi.location.service.LocationServiceImpl.getLocationById(LocationServiceImpl.java:91)
 at com.demo.myapi.location.service.LocationServiceTest.lambda$0(LocationServiceTest.java:178)
 ... 72 more

解决方案 #

问题分析 #

从错误栈可以看出，NullPointerException发生在orElseThrow的lambda表达式中，根源是业务方法中依赖的credentialService、messageServiceString、mapper以及测试用例中的headers都没有被Mock，处于null状态，调用它们的方法时直接抛出NPE，导致还没来得及返回CustomException就报错。

修复步骤 #

1. 在测试类中添加所有业务方法依赖的Mock对象：

@ExtendWith(MockitoExtension.class)
public class LocationServiceTest {
    @InjectMocks
    private LocationServiceImpl locationService;

    @Mock
    private LocationRepository locationRepository;
    // 添加以下Mock对象
    @Mock
    private CredentialService credentialService;
    @Mock
    private MessageServiceString messageServiceString;
    @Mock
    private YourMapperClass mapper; // 替换为实际的mapper类名
    @Mock
    private HttpHeaders headers;

2. 在测试方法中，对需要执行的无返回值方法做空操作Mock，避免调用时抛出异常：

@Test
void whenGetLocationById_thenReturnCustomException() {
    // Given
    when(locationRepository.findById(anyString())).thenReturn(Optional.empty());
    // 模拟credentialService的checkRegistered方法无操作
    doNothing().when(credentialService).checkRegistered(any(HttpHeaders.class));

    // When 
    CustomException exception = assertThrows(CustomException.class, () -> {
        // 替换anyString()为具体字符串，避免匹配器使用不一致问题
        locationService.getLocationById(headers, "test-location-id");
    });

    // Then
    assertEquals(ResponseEnum.UNKNOWN_LOCATION, exception.getException());
}

这样修改后，所有依赖都被正确Mock，不会触发NPE，业务代码会正常执行到抛出CustomException的逻辑，测试即可通过。

内容的提问来源于stack exchange，提问作者User