code: def test_register_for_llm_without_description():
      with pytest.MonkeyPatch.context() as mp:
          mp.setenv("OPENAI_API_KEY", "mock")
          agent = ConversableAgent(name="agent", llm_config={})
  
          with pytest.raises(ValueError) as e:
  
              @agent.register_for_llm()
              def exec_python(
                  cell: Annotated[str, "Valid Python cell to execute."]
              ) -> str:
                  pass
  
          assert (
              e.value.args[0]
              == "Function description is required, none found."
          )
  
imports: import asyncio
  import copy
  import sys
  import time
  from typing import Any, Callable, Dict, Literal
  import unittest
  import inspect
  import pytest
  from unittest.mock import patch
  from pydantic import BaseModel, Field
  from typing_extensions import Annotated
  import autogen
  from autogen.agentchat import ConversableAgent, UserProxyAgent
  from test_assistant_agent import KEY_LOC, OAI_CONFIG_LIST
  from conftest import skip_openai
label_desc: Use image node_id 15 for calling a global function with example usage: test_register_for_llm_without_description() without return types