@SpringBootTest vs @ExtendWith(SpringExtension.class)

When testing Spring applications, it's important to choose the right approach to load the application context and manage dependencies. Choosing the correct approach ensures that your tests are both efficient and effective. Loading the entire application context when it's not needed can slow down your tests and make them more brittle, as they become dependent on a larger set of configurations and beans. Conversely, not loading enough of the application context might result in tests that do not accurately reflect the production environment, leading to missed bugs and integration issues.

@SpringBootTest

Use @SpringBootTest when you need to load the full application context. This annotation is ideal for integration tests that require all beans and configurations to be available. It starts the entire Spring application context, including the web server if applicable, providing a comprehensive test environment similar to production.

Example:

@SpringBootTest
public class MyServiceIntegrationTest {

    @Autowired
    private MyService myService;

    @Test
    void testMyService() {
        assertNotNull(myService);
        // Additional assertions and test logic
    }
}

@ExtendWith(SpringExtension.class)

Use @ExtendWith(SpringExtension.class) for lightweight tests where you need Spring's dependency injection and test context features without having to necessarily load the entire application context. This annotation integrates the Spring TestContext Framework with JUnit 5, enabling you to use Spring's testing annotations and features within your tests. The context configuration can be specified using annotations such as @ContextConfiguration, @SpringBootTest, or other Spring test configuration annotations.

Example:

@ExtendWith(SpringExtension.class)
@ContextConfiguration(classes = TestConfig.class)
public class MyServiceTest {

    @Autowired
    private MyService myService;

    @Test
    void testMyService() {
        assertNotNull(myService);
        // Additional assertions and test logic
    }
}

Configuration Class:

@Configuration
public class TestConfig {

    @Bean
    public MyService myService() {
        return new MyServiceImpl();
    }
}

Key Differences

• @SpringBootTest: Loads the full application context, making it suitable for integration tests that require all beans and configurations.

• @ExtendWith(SpringExtension.class): Does not load any application context by itself. It allows for dependency injection and other Spring features in lightweight tests, and you need to specify the context configuration explicitly.

Note that @SpringBootTest already includes the annotation @ExtendWith(SpringExtension.class), so you don't need to specify both.

Summary

• Use @SpringBootTest for full application integration tests.

• Use @ExtendWith(SpringExtension.class) for more focused, lightweight tests that require dependency injection but not the entire application context.

By implementing the tests appropriately, you can avoid unnecessary load while running them, leading to more effective and efficient testing of your Spring applications and avoiding unnecessary productivity hits.