def METHOD_NAME(class_with_config, simple_config_spec):
    ConfigFile.save_config(class_with_config, {"a": 1})
    with open(ConfigFile.config_filename(class_with_config), "r") as f:
        assert f.read() == '{"a": 1}'
    assert ConfigFile.load_config(class_with_config, simple_config_spec) == {
        "a": 1,
        "b": 3,
    }