Spring Boot projects power many real-world applications, so robust testing is essential to ensure reliability and maintainability. In this chapter, you will discover how different testing strategies help you catch bugs early, verify business logic, and build confidence in your codebase. You will learn how to choose the right approach for each scenario, from quick unit tests to broader integration tests, making your Spring Boot applications stronger and easier to maintain.

Testing Strategies in Spring Boot

When building Spring Boot applications, you need to make sure each part works correctly. Different testing strategies help you check your code at different levels. Here are the main types:

Unit Testing

Unit testing checks individual pieces of your code, such as a single method or class, in isolation. You do not load the full Spring context, so tests run quickly.

Example:

• You write a test for a CalculatorService class to check if the add method returns the correct result.
• You use a tool like JUnit to run the test.
• You might use Mockito to mock dependencies.

@Test
void testAdd() {
    CalculatorService service = new CalculatorService();
    assertEquals(5, service.add(2, 3));
}

Integration Testing

Integration testing checks how different parts of your application work together. You usually load the Spring context, so beans and configuration are available.

Example:

• You test a UserService that depends on a UserRepository.
• You use @SpringBootTest to load the application context.

@SpringBootTest
class UserServiceIntegrationTest {
    @Autowired
    private UserService userService;

    @Test
    void testFindUser() {
        User user = userService.findUserById(1L);
        assertNotNull(user);
    }
}

End-to-End Testing

End-to-end (E2E) testing checks the whole application, including the database, web layer, and external services. These tests simulate real user actions.

Example:

• You use a tool like Selenium or RestAssured to send HTTP requests to your running application.
• You test the full workflow, such as creating a user through the API and checking the response.

@Test
void createUserApiTest() {
    given()
        .contentType("application/json")
        .body("{\"name\":\"Alice\"}")
    .when()
        .post("/users")
    .then()
        .statusCode(201);
}

Best Practices

• Write unit tests for business logic and keep them fast;
• Use integration tests to check how components interact;
• Reserve end-to-end tests for critical user flows;
• Name tests clearly so you understand what they check;
• Use test data that is easy to understand and maintain;
• Run tests automatically as part of your build process.