Testing Swiftmailer in a Silex app

MessageLogger.php

<?php

/*
 * This file is part of the Symfony package.
 *
 * (c) Fabien Potencier <fabien@symfony.com>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Logger;

/**
 * MessageLogger.
 *
 * @author Fabien Potencier <fabien@symfony.com>
 * @author Clément JOBEILI <clement.jobeili@gmail.com>
 */
class MessageLogger implements \Swift_Events_SendListener
{
    /**
     * @var array
     */
    protected $messages;

    public function __construct()
    {
        $this->messages = array();
    }

    /**
     * Get the message list
     *
     * @return array
     */
    public function getMessages()
    {
        return $this->messages;
    }

    /**
     * Get the message count
     *
     * @return int count
     */
    public function countMessages()
    {
        return count($this->messages);
    }

    /**
     * Empty the message list
     *
     */
    public function clear()
    {
        $this->messages = array();
    }

    /**
     * Invoked immediately before the Message is sent.
     *
     * @param \Swift_Events_SendEvent $evt
     */
    public function beforeSendPerformed(\Swift_Events_SendEvent $evt)
    {
        $this->messages[] = clone $evt->getMessage();
    }

    /**
     * Invoked immediately after the Message is sent.
     *
     * @param \Swift_Events_SendEvent $evt
     */
    public function sendPerformed(\Swift_Events_SendEvent $evt)
    {
    }
}

SwiftTest.php

<?php

use Silex\WebTestCase;

class SwiftTest extends WebTestCase
{
    public function createApplication()
    {
        $app = require __DIR__.'/../src/app.php';

        $app["swiftmailer.transport"] = new \Swift_Transport_NullTransport($app['swiftmailer.transport.eventdispatcher']);
        $app['mailer.logger'] = new Logger\MessageLogger();
        $app['mailer']->registerPlugin($app['mailer.logger']);
        return $app;
    }

    public function sendTest()
    {
       $client = $this->createClient();
       $crawler = $client->request('POST', '/', array("somedata"=>"to_send"));

       $this->assertEquals(1, $this->app['mailer.logger']->countMessages(), "Only one email sent");
       
       $emails = $this->app['mailer.logger']->getMessages();
       $this->assertEquals("This is my subject", $emails[0]->getSubject(), "Subject is correct");
    }
}