code: def test_files_are_optional(self):
      backend = LocalFilesystemBackend()
      assert None is backend.get_connection("CONN_A")
      assert backend.get_variable("VAR_A") is None
  
imports: from __future__ import annotations
  import json
  import os
  import re
  from contextlib import contextmanager
  from unittest import mock
  import pytest
  from airflow.configuration import ensure_secrets_loaded
  from airflow.exceptions import AirflowException, AirflowFileParseException, ConnectionNotUnique
  from airflow.models import Variable
  from airflow.secrets import local_filesystem
  from airflow.secrets.local_filesystem import LocalFilesystemBackend
  from tests.test_utils.config import conf_vars
label_desc: Use image node_id 4 for calling the TestLocalFileBackend obj's underlying member method code with example usage: obj.test_files_are_optional() without return types