$this->drupalPostForm(NULL, $edit, t('Upload'));
/** @var \Drupal\file\FileStorageInterface $file_storage */
$file_storage = $this->container->get('entity.manager')->getStorage('file');
$this->drupalPostForm(NULL, $edit, t('Upload'));
/** @var \Drupal\file\FileStorageInterface $file_storage */
$file_storage = $this->container->get('entity.manager')->getStorage('file');