code: def test_callback_handler_serialization():
      result = serialize_callback_handler(streaming_callback)
      assert result == "test_utils.streaming_callback"
  
imports: import pytest
  from haystack.components.generators.utils import default_streaming_callback
  from haystack.components.generators.utils import serialize_callback_handler, deserialize_callback_handler
label_desc: Use image node_id 2 for calling a global function with example usage: test_callback_handler_serialization() without return types