code: def test_callable_defer():
      config = Config()
      config.add("alias", lambda c: c.master_doc, "", str)
  
      assert config.master_doc == "index"
      assert config.alias == "index"
  
      config.master_doc = "contents"
      assert config.alias == "contents"
  
      config.master_doc = "master_doc"
      config.alias = "spam"
      assert config.alias == "spam"
  
imports: import pickle
  import time
  from pathlib import Path
  from unittest import mock
  import pytest
  import sphinx
  from sphinx.builders.gettext import _gettext_compact_validator
  from sphinx.config import ENUM, Config, _Opt, check_confval_types
  from sphinx.deprecation import RemovedInSphinx90Warning
  from sphinx.errors import ConfigError, ExtensionError, VersionRequirementError
label_desc: Use image node_id 9 for calling a global function with example usage: test_callable_defer() without return types