code: def streaming_callback_handler(x):
      return x
  
imports: from unittest.mock import patch, MagicMock, Mock
  import pytest
  from huggingface_hub.inference._text_generation import TextGenerationStreamResponse, Token, StreamDetails, FinishReason
  from huggingface_hub.utils import RepositoryNotFoundError
  from haystack.components.generators.chat import HuggingFaceTGIChatGenerator
  from haystack.dataclasses import StreamingChunk, ChatMessage
label_desc: Use image node_id 3 for calling a global function with example usage: streaming_callback_handler(x) and returns: x