code: def _get_key(ext, header):
      key = ext + "_" + ("h" if header else "nh")
      return key
  
imports: from __future__ import annotations
  import bz2
  import errno
  import filecmp
  import itertools
  import logging
  import shutil
  from gzip import GzipFile
  from tempfile import NamedTemporaryFile, mkdtemp
  from unittest import mock
  import pytest
  from airflow.exceptions import AirflowException
  from airflow.providers.apache.hive.transfers.s3_to_hive import S3ToHiveOperator
label_desc: Use image node_id 4 for calling the TestS3ToHiveTransfer obj's underlying member method code with example usage: obj._get_key(ext, header) and returns: key