code: def test_message_to_dict(self):
      # Test string message
      message_str = "Hello"
      expected_dict = {"content": [{"type": "text", "text": "Hello"}]}
      self.assertDictEqual(
          self.agent._message_to_dict(message_str), expected_dict
      )
  
      # Test list message
      message_list = [{"type": "text", "text": "Hello"}]
      expected_dict = {"content": message_list}
      self.assertDictEqual(
          self.agent._message_to_dict(message_list), expected_dict
      )
  
      # Test dictionary message
      message_dict = {"content": [{"type": "text", "text": "Hello"}]}
      self.assertDictEqual(
          self.agent._message_to_dict(message_dict), message_dict
      )
  
file_path: autogen/test/agentchat/contrib/test_lmm.py
imports: import unittest
  from unittest.mock import MagicMock
  import pytest
  import autogen
  from autogen.agentchat.agent import Agent
label_desc: Use image node_id 3 for calling the TestMultimodalConversableAgent obj's underlying member method code with example usage: obj.test_message_to_dict() without return types