Saturday, 5 February 2022

Spring boot - Testing Service Layer Code with JUnit 5 & Mockito | RESTful Web Services

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Testing Service Layer with JUnit 5 & Mockito

In a Spring Boot application, the Service Layer is where your core business logic lives. Testing this layer in isolation is crucial. This guide explains how to use JUnit 5 and Mockito to write fast, reliable unit tests that don't depend on a database or external services.

Why Mock the Repository?

Unit tests should be isolated. By using Mockito's @Mock, we create a "fake" version of our Repository. This allows us to:

Speed up tests: No need to wait for a database to start.
Avoid side effects: Tests won't change your actual data.
Test edge cases: Easily simulate scenarios like "user not found" or "database error."

Key Annotations

To set up your service layer tests, you'll primarily use these three annotations:

@Mock: Creates a mock instance of a dependency (like your Repository).
@InjectMocks: Creates an instance of the class being tested and injects the mocks into it.
@BeforeEach: A method that runs before every test case, usually to initialize the mocks.

Asserting Exceptions

A great test doesn't just check for success; it also verifies that your code handles errors correctly. With JUnit 5, you can use assertThrows to ensure your service throws the right exception when it encounters bad data.

        assertThrows(UsernameNotFoundException.class, () -> { 

            userService.getUser("wrong@email.com"); 

        });

📥 Download the Full Code!

I’ve provided the complete Java source code and PowerPoint presentation for this Service Layer tutorial! You can find the direct download links in the description of the YouTube video above.