code: def test_overrides():
      config = Config(
          {"value1": "1", "value2": 2, "value6": {"default": 6}},
          {
              "value2": 999,
              "value3": "999",
              "value5.attr1": 999,
              "value6.attr1": 999,
              "value7": "abc,def,ghi",
              "value8": "abc,def,ghi",
          },
      )
      config.add("value1", None, "env", ())
      config.add("value2", None, "env", ())
      config.add("value3", 0, "env", ())
      config.add("value4", 0, "env", ())
      config.add("value5", {"default": 0}, "env", ())
      config.add("value6", {"default": 0}, "env", ())
      config.add("value7", None, "env", ())
      config.add("value8", [], "env", ())
  
      assert config.value1 == "1"
      assert config.value2 == 999
      assert config.value3 == 999
      assert config.value4 == 0
      assert config.value5 == {"attr1": 999}
      assert config.value6 == {"default": 6, "attr1": 999}
      assert config.value7 == "abc,def,ghi"
      assert config.value8 == ["abc", "def", "ghi"]
  
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 6 for calling a global function with example usage: test_overrides() without return types