code: def test_register_pages_changed_callback(self):
      callback = lambda: None
  
      disconnect = source_util.register_pages_changed_callback(callback)
  
      source_util._on_pages_changed.connect.assert_called_once_with(
          callback, weak=False
      )
  
      disconnect()
      source_util._on_pages_changed.disconnect.assert_called_once_with(
          callback
      )
  
file_path: streamlit/lib/tests/streamlit/source_util_test.py
imports: import unittest
  from pathlib import Path
  from unittest.mock import MagicMock, patch
  import pytest
  from parameterized import parameterized
  import streamlit.source_util
  from streamlit.util import calc_md5
label_desc: Use image node_id 5 for calling the PageHelperFunctionTests obj's underlying member method code with example usage: obj.test_register_pages_changed_callback() without return types