Sulu\Component\Cache\CacheInterface::invalidate PHP Method

    public function invalidate();

 protected function setUp()
 {
     parent::setUp();
     $this->purgeDatabase();
     $this->em = $this->db('ORM')->getOm();
     $this->initOrm();
     $this->systemCollectionCache = $this->getContainer()->get('sulu_media.system_collections.cache');
     $this->systemCollectionConfig = $this->getContainer()->getParameter('sulu_media.system_collections');
     // to be sure that the system collections will rebuild after purge database
     $this->systemCollectionCache->invalidate();
 }