Adding test sources directory to the project

This step is needed as the Mojo Archetype (as of this writing) does not sets up test folder when we created our Maven plugin project.

1. To the project root add a directory src/test/java. We will create our unit tests under this location.
2. To the project root add a director src/test/resources. This directory will hold resources that we use for Mojo testing.

Adding plugin test harness dependency

1. First thing we need to do is to add the Maven plugin test harness dependency to our Plugin's pom.xml. Locate the pom.xml and add the harness dependency as follows.

     <dependencies>
       .
       .
       .
      <dependency>
         <groupId>org.apache.maven.shared</groupId>
         <artifactId>maven-plugin-testing-harness</artifactId>
         <version>1.0-beta-1</version>
         <scope>test</scope>
       </dependency>
     </dependencies>

2. Next we need to update depdendency references in our Eclipse project settings to make the plugin testing harness available. To do this run the following from the command prompt from the plugin project's directory.

    mvn eclipse:clean eclipse:eclipse

3. Refresh the Eclipse project by selecting the project root folder and pressing 'F5' key.

   You will see that the plugin testing harness dependency and the test directory that we added in the previous step are now updated.

Writing our Mojo unit tests

1. Create a new package org.codehaus.plexus to create our test in. Note that we create the package with the same name that our Mojo implementation resides in. This is a convenience to test out methods on Mojo which may have access specifiers that allow access only from within same package.
2. We write a couple of tests to ensure that our Mojo instance is being retrieved as expected, and to test that it executes without errors for a valid list of websites.

   Our test source looks as follows:

   public class MonitorMojoTest
       extends AbstractMojoTestCase
   {
   
       public void testMojoLookup()
           throws Exception
       {
           File pluginXml = new File( getBasedir(), "src/test/resources/unit/plugin-config.xml" );
           MonitorMojo mojo = (MonitorMojo) lookupMojo( "monitor", pluginXml );
           assertNotNull( mojo );
       }
   
       public void testMojoExecution()
           throws Exception
       {
           File pluginXml = new File( getBasedir(), "src/test/resources/unit/plugin-config.xml" );
           MonitorMojo mojo = (MonitorMojo) lookupMojo( "monitor", pluginXml );
           assertNotNull( mojo.getWebsites() );
           assertEquals( 1, mojo.getWebsites().size() );
           assertNotNull( mojo.getMonitor() );
           try
           {
               mojo.execute();
           }
           catch ( Exception e )
           {
               fail( "Unexpected exception with test data." );
           }
       }
   }

3. We set up a test configuration for the Mojo under src/test/resources/unit/plugin-config.xml (yes, that's the file that we refer to in the test above!).

   <project>
     <build>
       <plugins>
         <plugin>
           <groupId>org.codehaus.plexus</groupId>
           <artifactId>plexus-website-monitor-plugin</artifactId>
           <configuration>
             <websites>
               <website>http://plexus.codehaus.org/</website>
             </websites>
           </configuration>
         </plugin>
       </plugins>
     </build>
   </project>

4. Also our Mojo implementation is now updated to be as below:

   public class MonitorMojo
       extends AbstractMojo
   {
   
       /**
        * List of websites to monitor.
        * @parameter 
        */
       private List websites;
   
       /**
        * The website monitor component instance that will be injected 
        * by the Plexus runtime.
        * @component 
        */
       private WebsiteMonitor monitor;
   
       public void execute()
           throws MojoExecutionException, MojoFailureException
       {
           if ( !hasWebsites() )
           {
               if ( getLog().isWarnEnabled() )
                   getLog().warn( "No websites specified to be monitored." );
               return;
           }
   
           if ( getLog().isDebugEnabled() )
               showMonitoredWebsites();
   
           monitor.addWebsites( websites );
           try
           {
               monitor.monitor();
           }
           catch ( Exception e )
           {
               if ( getLog().isErrorEnabled() )
                   getLog().error( "Error monitoring websites.", e );
           }
       }
   
       private void showMonitoredWebsites()
       {
           getLog().debug( "Monitoring following websites:" );
           for ( Iterator it = websites.iterator(); it.hasNext(); )
           {
               String website = (String) it.next();
               getLog().debug( "\t" + website );
           }
       }
   
       /**
        * Determines if websites were specified to the Mojo.
        * 
        * @return <code>true</code> if there were websites specified.
        */
       private boolean hasWebsites()
       {
           return ( null != websites && websites.size() > 0 );
       }
   
       /**
        * Returns the list of websites.<p>
        * <em>Not public API. For unit tests only.</em>
        * 
        * @return List of websites specified via Mojo configuration.
        */
       protected List getWebsites()
       {
           return this.websites;
       }
   
       /**
        * Returns the {@link WebsiteMonitor} component instance.<p>
        * <em>Not public API. For unit tests only.</em>
        * 
        * @return the {@link WebsiteMonitor} instance.
        */
       protected WebsiteMonitor getMonitor()
       {
           return monitor;
       }
   
   }

5. Let's run the test and see what happens. You can run the test from within your favourite IDE, or from command prompt by typing

    mvn clean test 

   At this point, the Mojo test should run without any failures.

   Great! You have just hooked your Plexus component successfully to a Maven plugin.

   For more information on developing and using Maven plugins, please refer to Guide to Developing Java Plugins