code: def head_item(item_id: str):
      return JSONResponse(None, headers={"x-fastapi-item-id": item_id})
  
imports: from typing import Optional
  from dirty_equals import IsDict
  from fastapi import FastAPI
  from fastapi.responses import JSONResponse
  from fastapi.testclient import TestClient
  from pydantic import BaseModel
label_desc: Use image node_id 4 for calling a global function with example usage: head_item(item_id) and returns: JSONResponse