Verify custom JUnit extension logs test start and end

Preconditions (2)

Step 1: Create a test class and register the custom extension using @ExtendWith

Step 2: Write a simple test method that asserts true is true

Step 3: Run the test class

Step 4: Observe the console output for logs from the custom extension indicating test start and test end

✅ Expected Result: The console shows log messages from the custom extension before and after the test method runs, and the test passes

Automation Requirements - JUnit 5

Assertions Needed:

Assert that the test method passes successfully

Verify via console output that the extension logs test start and end

Best Practices:

Use @ExtendWith annotation to register the extension

Implement BeforeTestExecutionCallback and AfterTestExecutionCallback interfaces in the extension

Keep test methods simple and focused

Use standard JUnit assertions

Automated Solution

JUnit

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.junit.jupiter.api.extension.BeforeTestExecutionCallback;
import org.junit.jupiter.api.extension.AfterTestExecutionCallback;
import org.junit.jupiter.api.extension.ExtensionContext;

import static org.junit.jupiter.api.Assertions.assertTrue;

class LoggingExtension implements BeforeTestExecutionCallback, AfterTestExecutionCallback {
    @Override
    public void beforeTestExecution(ExtensionContext context) {
        System.out.println("[Extension] Starting test: " + context.getDisplayName());
    }

    @Override
    public void afterTestExecution(ExtensionContext context) {
        System.out.println("[Extension] Finished test: " + context.getDisplayName());
    }
}

@ExtendWith(LoggingExtension.class)
public class CustomExtensionTest {

    @Test
    void simpleTest() {
        assertTrue(true, "True should be true");
    }
}

The LoggingExtension class implements two JUnit 5 extension interfaces: BeforeTestExecutionCallback and AfterTestExecutionCallback. These allow it to run code before and after each test method.

Inside beforeTestExecution, it prints a message indicating the test is starting. Inside afterTestExecution, it prints a message indicating the test finished.

The test class CustomExtensionTest uses @ExtendWith(LoggingExtension.class) to register the extension. It has one simple test method simpleTest that asserts true is true.

When running the test, the console will show the extension's log messages before and after the test method runs, confirming the extension works. The test assertion ensures the test passes.

Common Mistakes - 3 Pitfalls

Not registering the extension with @ExtendWith annotation

Implementing the wrong extension interfaces

Using System.out.println in production extensions without proper logging

Bonus Challenge

Modify the custom extension to measure and log the duration of each test execution

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