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Discover how to effectively mock a repository in a Spring Boot service test to avoid null references during execution.
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This video is based on the question https://stackoverflow.com/q/63933206/ asked by the user 'Susmitha Thallapally' ( https://stackoverflow.com/u/4596918/ ) and on the answer https://stackoverflow.com/a/63933620/ provided by the user 'Gavin' ( https://stackoverflow.com/u/4187837/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Fix a Null Mocked Repository in Your Spring Boot Service Testing

When writing tests for your Spring Boot applications, you might encounter the frustrating problem of a mocked repository being null during execution. This can throw your tests off track and lead to confusion about where things are going wrong. In this post, we'll explore a common scenario that leads to this issue and guide you through a solid solution.

The Problem Description

You may find yourself in a situation where you're using a service called HRfeedService, which relies on an interface HRfeedRepository to fetch data. In your test class, you aim to mock this repository so that it provides predefined responses when its methods are called.

Here's a simplified example of your service and repository:

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Your test class looks something like this:

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As you may have noticed, the hRfeedRepository in HRfeedService remains null during the test, which leads to unexpected behavior.

The Solution

The key issue here is that in your test setup, you did not correctly inject the mocked HRfeedRepository into the HRfeedService. In traditional Spring applications, this injection is managed by the Spring framework. When testing, you'll need to set it up yourself.

Solution 1: Constructor Injection

A straightforward fix involves using constructor injection for your service. Here's how you can modify your HRfeedService:

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This way, you can easily provide the mocked repository during your test setup:

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Solution 2: Using Spring's Test Infrastructure

Alternatively, if you prefer, you can utilize Spring’s test infrastructure to manage your beans, which can be more convenient especially for larger applications. You can annotate your test class with @ SpringBootTest or @ RunWith(SpringRunner.class) to let Spring take care of everything:

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This configuration enables you to mock your repository without needing to modify the HRfeedService class.

Conclusion

In summary, injecting dependencies correctly in your test cases is crucial to ensuring reliable mocking and testing in Spring Boot applications. By using constructor injection or allowing Spring to handle the beans, you can resolve the issue of null repositories and improve the robustness of your tests.

Next time you find yourself struggling with null references in your mocked repositories, try the solutions outlined above to keep your tests running smoothly.