JUnit Test Listener: JUnit 4 RunListener Example

JUnit Test Listeners allow us to listen to the events that occur during the execution of tests. These events include the start and end of tests, test failures, test assumptions, and more. Listeners can be useful for reporting, logging, or executing custom logic when tests run.

JUnit also provides support for adding listeners while executing the tests via the RunListener class. This listener can be used for various purposes from improved logging to test specific logic.

1. JUnit RunListener Example

In JUnit 4, we can create a test listener by extending the RunListener class and overriding its method to inject the custom code.

Let’s see an example.

1.1. JUnit Test

We are writing two test classes below for example only. We will monitor the logs printed for tests written in these classes.

public class TestFeatureOne {

	@Test
	public void testFirstFeature(){
		Assert.assertTrue(true);
	}
}

public class TestFeatureTwo {

	@Test
	public void testSecondFeature() {
		Assert.assertTrue(true);
	}

	@Test
	@Ignore
	public void testSecondFeatureIngored() {
		Assert.assertTrue(true);
	}
}

1.2. JUnit Test Listener Class

Let’s write run listener. This listener will extend the RunListener class provided by JUnit.

We are free to override any number of methods RunListener class from including no method at all.

import org.junit.runner.Description;
import org.junit.runner.Result;
import org.junit.runner.notification.Failure;
import org.junit.runner.notification.RunListener;
 
public class ExecutionListener extends RunListener
{
  /**
   * Called before any tests have been run.
   * */
  public void testRunStarted(Description description) throws java.lang.Exception {
    System.out.println("Number of tests to execute : " + description.testCount());
  }
 
  /**
   *  Called when all tests have finished
   * */
  public void testRunFinished(Result result) throws java.lang.Exception {
    System.out.println("Number of tests executed : " + result.getRunCount());
  }
 
  /**
   *  Called when an atomic test is about to be started.
   * */
  public void testStarted(Description description) throws java.lang.Exception {
    System.out.println("Starting execution of test case : "+ description.getMethodName());
  }
 
  /**
   *  Called when an atomic test has finished, whether the test succeeds or fails.
   * */
  public void testFinished(Description description) throws java.lang.Exception {
    System.out.println("Finished execution of test case : "+ description.getMethodName());
  }
 
  /**
   *  Called when an atomic test fails.
   * */
  public void testFailure(Failure failure) throws java.lang.Exception {
    System.out.println("Execution of test case failed : "+ failure.getMessage());
  }
 
  /**
   *  Called when a test will not be run, generally because a test method is annotated with Ignore.
   * */
  public void testIgnored(Description description) throws java.lang.Exception {
    System.out.println("Execution of test case ignored : "+ description.getMethodName());
  }
}

2. Demo

Now, let’s run the tests and observe the listener output.

import org.junit.runner.JUnitCore;
import com.howtodoinjava.junit.TestFeatureOne;
import com.howtodoinjava.junit.TestFeatureTwo;
 
public class ExecuteWithRunListener {

  public static void main(String[] args)  {

    JUnitCore runner = new JUnitCore();
    runner.addListener(new ExecutionListener());
    runner.run(TestFeatureOne.class, TestFeatureTwo.class);
  }
}

Program Output.

Number of tests to execute : 3

Starting execution of test case : testFirstFeature
Finished execution of test case : testFirstFeature

Starting execution of test case : testSecondFeature
Finished execution of test case : testSecondFeature

Execution of test case ignored : testSecondFeatureIngored
Number of tests executed : 2

Clearly, adding a listener provides extra control on test execution with improved logging support.

Happy Learning !!