JUnit Listeners are classes which receive callbacks about test execution. These callbacks are executed  when there is any event in test execution lifecycle like just before the test has started execution, just after the test has finished, when the test has failed or when the test have passed.  The callbacks are very useful in implementing functionality like logging about the tests, preparing customized reports an filtering test results. In this article we will show how the JUnit listeners are configured.

There are couple of ways this can be configured:

1. In a declarative way by using the maven-surefire-plugin
2. In a programmatic way using JUnit APIs

Now whether we use maven-surefire-plugin or JUnit API, we need to create a class which extends a class RunListener

Here is the listener class :

package com.codereq.test;

import org.junit.runner.Description;
import org.junit.runner.Result;
import org.junit.runner.notification.RunListener;

public class CommonListener extends RunListener {

    public void testStarted(Description description) {
        System.out.println("\n\n\nStarting .... " + description.getMethodName());
    }

    public void testFinished(Description description) {
        System.out.println("Finished .... "+ description.getMethodName());
    }

    public void testRunFinished(Result result) {
        System.out.println("\n\n");
    }
}

Configuring maven-surefire-plugin

In the standard maven pom.xml, the maven-surefire-plugin is configured by adding a listener property with the name of the class extending the RunListener class

<build>
    <plugins>
        <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-surefire-plugin</artifactId>
    <version>2.19.1</version>
            <configuration>
 <properties>
     <property>
                 <name>listener</name>
 <value>com.codereq.test.CommonListener</value>
     </property>
 </properties>
    </configuration>
        </plugin>
    </plugins>
</build>

This is most commonly used pattern to add a listener and execute tests.

Configuring JUnit Runner

Another way to configure the JUnit listener is to register the listener class with JUnitCore. Here is the example:

import org.junit.runner.JUnitCore;

public class MyTestRunner {
    public static void main(String args[]) {
        JUnitCore runner = new JUnitCore();
runner.addListener(new MyTestListener());
runner.run(SampleTest.class);
    }
}

SampleTest.java

import org.junit.Assert;
import org.junit.Test;

public class SampleTest {

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

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

On execution of the MyTestRunner, you will get report like this:

Tests count : 2
Starting Test : process
Finishing Test : process
Starting Test : compute
Finishing Test : compute

So, these are the two ways JUnit listener can be configured.