docstr: Test a complete LangChain Agent run using StreamlitCallbackHandler.
docstr_tok: ["Test","a","complete","LangChain","Agent","run","using","StreamlitCallbackHandler","."]
file_path: streamlit/lib/tests/streamlit/external/langchain/streamlit_callback_handler_test.py
imports: from __future__ import annotations
  import unittest
  from pathlib import Path
  from unittest.mock import MagicMock
  import pytest
  import semver
  from google.protobuf.json_format import MessageToDict
  import streamlit
  from tests.delta_generator_test_case import DeltaGeneratorTestCase
label_desc: Use image node_id 1 for calling the StreamlitCallbackHandlerTest obj's underlying member method code with example usage: obj.test_agent_run() without return types