Mailer service mocking for Symfony2

ContactControllerTest.php

<?php

namespace Nelmio\HomeBundle\Tests\Controller;

use Nelmio\HomeBundle\Controller\ContactController;
use Liip\FunctionalTestBundle\Test\WebTestCase;

class ContactControllerTest extends WebTestCase
{
    public function testEmail()
    {
        $client = $this->createClient();
        $crawler = $client->request('GET', '/contact');
        $form = $crawler->selectButton('submit')->form();
        $form['contact[name]'] = 'Test';
        $form['contact[email]'] = 'test@example.org';
        $form['contact[message]'] = 'Test message';

        $client->submit($form);
        $response = $client->getResponse();

        $collector = $client->getProfile()->getCollector('swiftmailer');
        $this->assertEquals(1, $collector->getMessageCount());
        list($mail) = $collector->getMessages();

        $this->assertEquals(302, $response->getStatusCode());
        $this->assertTrue($mail instanceof \Swift_Message);
        $this->assertContains('Test message', $mail->getBody());
        $this->assertContains('test@example.org', $mail->getBody());
        $this->assertEquals(array('hello@nelm.io' => ''), $mail->getTo());
        $this->assertEquals('/contact/thanks', $response->headers->get('Location'));
    }
}