'File storage returns a tuple containing directories and files.'

def test_listdir(self):

    self.assertFalse(self.storage.exists('storage_test_1'))
    self.assertFalse(self.storage.exists('storage_test_2'))
    self.assertFalse(self.storage.exists('storage_dir_1'))
    self.storage.save('storage_test_1', ContentFile('custom    content'))
    self.storage.save('storage_test_2', ContentFile('custom    content'))
    os.mkdir(os.path.join(self.temp_dir, 'storage_dir_1'))
    (dirs, files) = self.storage.listdir('')
    self.assertEqual(set(dirs), {'storage_dir_1'})
    self.assertEqual(set(files), {'storage_test_1', 'storage_test_2'})
    self.storage.delete('storage_test_1')
    self.storage.delete('storage_test_2')
    os.rmdir(os.path.join(self.temp_dir, 'storage_dir_1'))
