使用Mockito doReturn始终返回null

Question

我在测试课上使用Mockito：

@RunWith(SpringRunner.class)
@Import({MyTestContextConfiguration.class})
public class MyWorkerTest extends BaseWorkerTest {

    @Spy
    protected static MyWorkerImpl externalTaskTopicServiceImpl;

    @Before
    @SneakyThrows
    public void setUp() {
        final Similarity similarity0 = Similarity.builder()
        .automatic(Boolean.TRUE)
        .score(0.555D)
        .build();

        final MyRequest mpr = MyRequest.builder()
        .reference(prod)
        .build();

        Mockito.doReturn(similarity0).when(externalTaskTopicServiceImpl).invokeMyService(mpr);
        //Mockito.when(ReflectionTestUtils.invokeMethod(externalTaskTopicServiceImpl, "invokeMyService", mpr)).thenReturn(similarity0);

    }

    @SneakyThrows
    @Test
    public void myTest() {
        ...
        externalTaskTopicServiceImpl.handle(externalTaskService, externalTask);
    }
}

MyRequest和Similarity是由ObjectMapper作为JSON处理的简单POJO。

工人impl类：

@Service
@Slf4j
public class MyWorkerImpl extends WorkerBase {
    @Override
    public void handle() {
        ...
        final MyRequest mpr = MyRequest.builder().reference(product).build();
        invokeMatchProductsService(mpr);
    }

    protected Similarity invokeMyService(final MyRequest req) throws MyServiceException {
        return httpService.matchPopResult(req);
    }
}

当我使用invokeMatchProductsService表示法时，null总是返回Mockito.doReturn()。当我使用Mockito.when()表示法时，返回一个Similarity对象，但最后测试用例失败了：

org.mockito.exceptions.misusing.WrongTypeOfReturnValue: 
Similarity cannot be returned by toString()
toString() should return String
***
If you're unsure why you're getting above error read on.
Due to the nature of the syntax above problem might occur because:
1. This exception *might* occur in wrongly written multi-threaded tests.
   Please refer to Mockito FAQ on limitations of concurrency testing.
2. A spy is stubbed using when(spy.foo()).then() syntax. It is safer to stub spies - 
   - with doReturn|Throw() family of methods. More in javadocs for Mockito.spy() method.

任何人都可以告诉我为什么在使用doReturn（）时我总是得到null，因为间谍是间谍？

Answer 1

如果你知道如何正确地做到这一点，那就不难了！ ;-)

而不是以这种方式存根：

Mockito.doReturn(similarity0).when(externalTaskTopicServiceImpl).invokeMyService(mpr);

你必须使用Matchers，或者更准确地说，是ArgumentMatchers：

Mockito.doReturn(similarity0).when((MyWorkerImpl)externalTaskTopicServiceImpl).invokeMyService(ArgumentMatchers.any(MyRequest.class));

很明显，错误的存根会导致null，因为在监视externalTask​​TopicServiceImpl时，仅在测试用例中/在本地定义的mpr将永远不会在程序执行期间使用。这避免了invokeMyService()中的空值。

关于org.mockito.exceptions.misusing.WrongTypeOfReturnValue，这只是我的设计错误：我在spied类中设计了返回ConcurrentHashMap<String, Object>的方法但是在测试用例中我返回了一个响应对象。