code: def _validate_file_mode(mode, file_name, optional=False):
      
      try:
          ownership = _stat(file_name)
      except subprocess.CalledProcessError as e:
          print("Error reading file: {}".format(e))
          if not optional:
              assert False, "Specified file does not exist: {}".format(file_name)
      assert mode == ownership.mode, \
          "{} has an incorrect mode: {} should be {}".format(
              file_name, ownership.mode, mode)
      print("Validate mode of {}: PASS".format(file_name))
docs: Validate that a specified file has the specified permissions.
  
      :param mode: file mode that is desires
      :type owner: str
      :param file_name: Path to the file to verify
      :type file_name: str
      :param optional: Is this file optional,
                       ie: Should this test fail when it's missing
      :type optional: bool