Custom extensions in JUnit - Framework Patterns

Framework Mode - Custom extensions

Folder Structure

src/
├── main/
│   └── java/
│       └── com/example/extensions/   # Custom JUnit extensions
│           ├── RetryExtension.java
│           └── TimingExtension.java
└── test/
    └── java/
        └── com/example/tests/         # Test classes using extensions
            └── SampleTest.java

Test Framework Layers

• Custom Extensions Layer: Contains reusable JUnit extension classes implementing interfaces like BeforeEachCallback, AfterEachCallback, or TestExecutionExceptionHandler.
• Test Layer: Test classes that use @ExtendWith annotation to apply custom extensions.
• Utilities Layer: Helper classes or methods used by extensions or tests (e.g., logging, retry logic).
• Configuration Layer: Properties or environment settings that can influence extension behavior (e.g., retry count).

Configuration Patterns

• Use java.util.Properties or System.getProperty to configure extension parameters like retry count or timeout.
• Allow environment variables or Maven/Gradle profiles to override default extension settings.
• Keep configuration centralized in a config.properties file or dedicated config class.
• Pass configuration values to extensions via constructor injection or static access.

Test Reporting and CI/CD Integration

• JUnit extensions can log additional info (e.g., retry attempts, test duration) to console or files.
• Integrate with CI tools (Jenkins, GitHub Actions) to capture test results including extension effects.
• Use JUnit XML reports to show retries or failures clearly.
• Extensions can add tags or metadata to tests for filtering in reports.

Best Practices for Custom Extensions

• Keep extensions focused on a single responsibility (e.g., retry, timing, logging).
• Use JUnit 5 extension interfaces properly (e.g., BeforeEachCallback, AfterTestExecutionCallback).
• Make extensions configurable and reusable across multiple test classes.
• Handle exceptions gracefully inside extensions to avoid masking test failures.
• Document extension usage clearly for test developers.

Self Check

Where in this folder structure would you add a new extension that logs test start and end times?

Key Result

Organize custom JUnit extensions in a dedicated package and apply them via @ExtendWith for reusable, configurable test behavior.