TestWatcher for reporting in JUnit - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this TestWatcher override?

Consider this JUnit 5 TestWatcher extension code. What will be printed when the test fails?

JUnit

import org.junit.jupiter.api.extension.TestWatcher;
import org.junit.jupiter.api.extension.ExtensionContext;

public class MyWatcher implements TestWatcher {
    @Override
    public void testFailed(ExtensionContext context, Throwable cause) {
        System.out.println("Test failed: " + context.getDisplayName());
    }
}

// Assume this watcher is registered for a test named "exampleTest" which fails.

A Test failed: exampleTest

B Test failed: null

C No output printed

D Compilation error due to missing method

💡 Hint

The testFailed method prints the test name on failure.

The testFailed method is called on test failure and prints the display name of the test, which is 'exampleTest'.

❓ assertion

intermediate

Which assertion correctly verifies a test was skipped using TestWatcher?

You want to assert inside a TestWatcher that a test was skipped. Which assertion is correct?

JUnit

import org.junit.jupiter.api.extension.TestWatcher;
import org.junit.jupiter.api.extension.ExtensionContext;
import java.util.Optional;

public class SkipWatcher implements TestWatcher {
    @Override
    public void testSkipped(ExtensionContext context, Optional<String> reason) {
        // Which assertion below is correct?
    }
}

A assertFalse(reason.isPresent());

B assertEquals("Skipped", reason.get());

C assertTrue(reason.isPresent());

D assertNull(reason);

💡 Hint

The reason parameter is Optional and should be present if skipped.

The reason parameter is an Optional containing the skip reason. It should be present when a test is skipped.

🔧 Debug

advanced

Why does this TestWatcher not print on test success?

This TestWatcher override does not print anything when a test passes. Why? public class SilentWatcher implements TestWatcher { @Override public void testSuccessful(ExtensionContext context) { // Intentionally left blank } }

A Because testSuccessful is never called on success

B Because ExtensionContext is null on success

C Because TestWatcher requires calling super.testSuccessful() to print

D Because testSuccessful method is empty, no output is printed

💡 Hint

Check what the method implementation does.

The testSuccessful method is called on success but since it is empty, no output occurs.

🧠 Conceptual

advanced

What is the main purpose of TestWatcher in JUnit 5?

Choose the best description of what TestWatcher is used for in JUnit 5 testing.

A To replace assertions inside test methods

B To monitor test lifecycle events and perform actions on test success, failure, or skip

C To configure test execution order

D To mock dependencies during tests

💡 Hint

Think about what events TestWatcher listens to.

TestWatcher listens to test lifecycle events like success, failure, and skip to allow custom reporting or actions.

❓ framework

expert

How to register a TestWatcher extension for all tests in a class?

You want to apply a TestWatcher implementation to all tests in a JUnit 5 test class. Which is the correct way?

A @ExtendWith(MyWatcher.class) on the test class

B Implement TestWatcher interface in the test class directly

C Call MyWatcher.testFailed() manually in each test

D Register MyWatcher in a static block inside the test class

💡 Hint

JUnit 5 uses annotations to register extensions.

The @ExtendWith annotation registers the TestWatcher extension for all tests in the class.