I have always used @Mock and @injectMock in java test classes. I came in a weird situation today. When I do @mock for WebTestClient then it gives me null pointer exception saying that it has a possibility to be null.
And when I change the annotation to @Autowire, it works as expected.
Pls let me know why is @mock not working in above case. I apologize if the question is really stupid to ask here.
I am trying to test a controller that returns Flux<Integer>.
Also pls answer this for me:
- Is it a good practice to use @Autowired in test classes or we only use it in special cases?
I was expecting using mock should not give me NPE.
>Solution :
@Mock and @Autowired annotations in Spring and why @Mock might not be working in your case.
@Mock is a Mockito annotation used to create a mock object of a class or interface. Mock objects are used to replace real objects in unit tests to isolate the code under test from its dependencies. Mock objects allow us to test the behavior of a class or method without depending on the behavior of its collaborators.
@Autowired is a Spring annotation used for dependency injection. When Spring sees the @Autowired annotation, it will look for a bean of the same type as the annotated field and inject it automatically. In other words, it is used to wire up the dependencies of a class.
Now, coming to your specific scenario, it seems like you’re trying to test a Spring WebFlux controller that returns a Flux and you’re using a WebTestClient to perform the test. The reason why @Mock might not be working for you is that WebTestClient is a Spring component and is created by Spring when the application context is initialized. Since Mockito doesn’t have access to the Spring container, it can’t create a mock of WebTestClient and inject it into your test class. Hence, when you try to use the mock, it gives you a null pointer exception.
On the other hand, @Autowired works because it is Spring’s own dependency injection mechanism and it has access to the Spring container. When you use @Autowired to inject a WebTestClient instance into your test class, Spring will create an instance of WebTestClient and inject it for you, allowing you to use it in your test.
Regarding your second question, it is generally a good practice to use @Mock and Mockito to mock dependencies in unit tests, rather than relying on real objects. This ensures that the tests are isolated and do not depend on the behavior of other components. However, there might be cases where it makes sense to use @Autowired, for example, if you need to test the integration of multiple components. Ultimately, the choice of using @Mock or @Autowired depends on the specific scenario and your testing requirements.
Yes, it is common to use the @Autowired annotation in Java test classes when you need to inject dependencies into the test. The @Autowired annotation is part of Spring’s dependency injection framework, which is commonly used in Java projects.
Using @Autowired in your test class can simplify your code by allowing Spring to inject dependencies into the test automatically, rather than manually creating instances of dependencies or mock objects. This can save time and reduce the likelihood of errors.
However, keep in mind that using @Autowired may not always be the best approach for testing. In some cases, you may need more fine-grained control over the dependencies used in a test and may need to manually create mock objects or other test doubles. Additionally, when using @Autowired, it’s important to make sure that the dependencies being injected are appropriate for the specific test and do not introduce unintended side effects.
In summary, using @Autowired in Java test classes can be a useful tool for dependency injection and simplifying your testing code, but it should be used judiciously and in a way that is appropriate for the specific test scenario.