Mockito: Inject real objects into private @Autowired fields

🧪 Testing Made Easy: Injecting Real Objects into Private @Autowired Fields with Mockito

Have you ever found yourself needing to inject real objects into private @Autowired fields during testing with Mockito? Maybe you've been using the @Mock and @InjectMocks annotations to inject dependencies into your test class, but now you want to go a step further and inject actual objects. Good news! It's indeed possible, and I'm here to show you how. Let's dive in!

The Dilemma

The scenario is simple: you have a class, let's call it Demo, with a private @Autowired field, SomeService. In your test class, DemoTest, you are already using Mockito's @Mock and @InjectMocks annotations to inject mocked dependencies into Demo. But now you're wondering if it's possible to inject real SomeService objects into Demo without exposing the field or creating a setter method.

@RunWith(MockitoJUnitRunner.class)
public class DemoTest {
    @Mock
    private SomeService service;

    @InjectMocks
    private Demo demo;

    // ...
}

public class Demo {
    @Autowired
    private SomeService service;

    // ...
}

The Solution

The good news is that Mockito provides a way to achieve this by using the @Spy annotation in combination with the @InjectMocks annotation. Here's how you can modify your code to inject real objects instead of mocks:

@RunWith(MockitoJUnitRunner.class)
public class DemoTest {
    @Spy
    @Autowired
    private SomeService service;

    @InjectMocks
    private Demo demo;

    // ...
}

By changing @Mock to @Spy in your DemoTest class, Mockito will create a spy object that preserves the original functionality of SomeService, allowing you to work with real instances of the class.

Putting It into Context

Let's take a closer look at what's happening here. When using @Mock, Mockito replaces the SomeService field in Demo with a mock object during testing. This is handy when you want fine-grained control over the behavior of the dependency. However, if you want to work with the actual object, using the @Spy annotation along with @Autowired allows you to achieve just that.

Engage with the Community

Testing can be a complex topic, and sometimes it's challenging to find the best approach. That's why we encourage you to share your thoughts, experiences, and questions in the comments below. Engage with our vibrant community of tech enthusiasts, learn from their insights, and contribute to the collective knowledge.

Are there any other testing scenarios you'd like us to explore in future blog posts? Let us know! We're here to help you on your journey to becoming a testing pro.

So go ahead, put this solution to the test, and let us know how it works for you. Happy testing!

🔍💻🧪