code: def test_dash_env_vars(empty_environ):
      assert {None} == {
          val for _, val in DASH_ENV_VARS.items()
      }, "initial var values are None without extra OS environ setting"
  
imports: import os
  import logging
  import pytest
  from flask import Flask
  from dash import Dash, exceptions
  from dash._configs import pathname_configs, DASH_ENV_VARS, get_combined_config, load_dash_env_vars
  from dash._utils import AttributeDict
  from dash._get_paths import app_get_asset_url, app_get_relative_path, app_strip_relative_path, get_asset_url, get_relative_path, strip_relative_path
label_desc: Use image node_id 1 for calling a global function with example usage: test_dash_env_vars(empty_environ) without return types