Understanding Why @TestConfiguration Does Not Override Beans in Spring Boot Integration Tests

Why is the @TestConfiguration bean in Spring Boot not overriding the bean defined in @Configuration during integration tests?

@Configuration
public class MyBeanConfig {
    @Bean
    public String configPath() {
        return "../production/environment/path";
    }
}

@TestConfiguration
public class MyTestConfiguration {
    @Bean
    @Primary
    public String configPath() {
        return "/test/environment/path";
    }
}

@Component
public class MyParsingComponent {
    private String CONFIG_PATH;
    
    @Autowired
    public void setCONFIG_PATH(String configPath) {
        this.CONFIG_PATH = configPath;
    }
}

In Spring Boot applications, the `@TestConfiguration` annotation is typically used for setting up test-specific beans that should override the existing ones defined in the main application context. However, there are common pitfalls that may prevent your `@TestConfiguration` beans from being recognized as overrides during integration tests.

@SpringBootTest
class MyIntegrationTest {

    @Autowired
    private MyParsingComponent myParsingComponent;

    @Test
    public void testConfigPath() {
        assertEquals("/test/environment/path", myParsingComponent.getCONFIG_PATH());
    }
}

Causes

• The `@TestConfiguration` class is not picked up by the Spring context during tests due to incorrect test setup.
• The primary annotation is not working as expected because of the way the application context is loaded; it may not be recognizing the configuration class as an overriding configuration.
• Multiple application contexts are being loaded, and the test context is not overlapping with the main context.

Solutions

• Ensure that your test class is annotating the Spring context properly using `@SpringBootTest`, which will enable the loading of your `@TestConfiguration`.
• Make sure you are using the `@Primary` annotation correctly if there are multiple beans of the same type, as it gives priority to that bean when autowiring.
• Check your test context configuration; it might be incorrectly set up, leading to the main application context overriding the test configuration.

Mistake: Forgetting to annotate the test class with `@SpringBootTest` leading to the annotation not being picked up.

Solution: Always use `@SpringBootTest` to ensure Spring Boot initializes the context correctly for your tests.

Mistake: Incorrectly using the `@Primary` annotation; not understanding its purpose.

Solution: Ensure you understand the role of `@Primary`. It should only be used when you have multiple beans of the same type.