docs: def isdir(path, message):
      """
      Raise an exception if the given directory does not exist.
  
      :param path: The path to a directory to be tested
      :param message: A custom message to report in the exception
  
      :raises: FileNotFoundError
      """
      if not os.path.isdir(path):
          raise FileNotFoundError(
              errno.ENOENT,
              "{}: {}".format(message, os.strerror(errno.ENOENT)), path)