How to get the current logged user in unit test?

I have this unit test :

class ProjectControllerTest extends WebTestCase
{

    private $client = null;
    private $user = null;
    private $projectName = null;
    private $em;

    public function setUp()
    {
        $this->client = static::createClient();
        $this->user = new User;
        $this->createAuthorizeClient($this->client);

        static::$kernel = static::createKernel();
        static::$kernel->boot();
        $this->em = static::$kernel->getContainer()->get('doctrine.orm.entity_manager');
    }

    public function testProjectNameEdition()
    {
        $project = new Project();
        $project
            ->setName(uniqid())
            ->setComment('test')
        ;
        $this->em->persist($project);
        $this->em->flush();

        $crawler = $this->client->request('GET', '/project/' . $project->getId() . '/edit');
        $form = $crawler->selectButton('codex_gui_project_submit')->form();
        $form['codex_gui_project[name]'] = $this->projectName . '1';
        $this->client->submit($form);

        $editProject = $this->em->getRepository('AcmeFooBundle:Project')->findOneByName($oldProjectName . '1');
        $this->assertEquals($this->projectName . '1', $editProject->getName());
    }

    public function createAuthorizeClient($client)
    {
        $container = static::$kernel->getContainer();
        $session = $container->get('session');
        $user = self::$kernel
            ->getContainer()->get('doctrine')
            ->getRepository('AcmeFooBundle:User')
            ->findOneByUsername('Nico')
        ;
        $token = new UsernamePasswordToken($user, $user->getUserName(), 'main', $user->getRoles());

        $session->set('_security_main', serialize($token));
        $session->save();
        $client->getCookieJar()->set(new Cookie($session->getName(), $session->getId()));

        return $client;
    }
}

Then when the new entity is persisted, the current user is getting in the ProjectListenner :

class ProjectListener
{

    protected $container;

    public function __construct(ContainerInterface $container)
    {
        $this->container = $container;
    }

    /**
     * Prepersist a creation of project
     *
     * @param \Doctrine\ORM\Event\LifecycleEventArgs $args
     */
    public function prePersist(LifecycleEventArgs $args)
    {
        $entity = $args->getEntity();

        if ($entity instanceof Project) {
            // Save the user and the created date
            $usr = $this->container->get('security.context')->getToken()->getUser();
            $entity->setCreated(new \DateTime());
            $entity->setCreator($usr);
    }
}

So this error happened when I run the test :

...PHP Fatal error: Call to a member function getUser() on a non-object in /var/www/codex_gui/vendor/acme/foo/Acme/foo/fooBundle/Listener/ProjectListener.php on line 32