code: def test_default_headers_option() -> None:
      assert openai.default_headers == None
  
      openai.default_headers = {"Foo": "Bar"}
  
      assert openai.default_headers["Foo"] == "Bar"
      assert openai.completions._client.default_headers["Foo"] == "Bar"
  
imports: from __future__ import annotations
  import os
  import httpx
  import pytest
  from httpx import URL
  import openai
  from openai import DEFAULT_TIMEOUT, DEFAULT_MAX_RETRIES
  import contextlib
  from typing import Iterator
  from openai.lib.azure import AzureOpenAI
label_desc: Use image node_id 6 for calling a global function with example usage: test_default_headers_option() without return types