code: def test_xcom_key_getitem(self, dag_maker):
      python_op = build_python_op(dag_maker)
      actual = XComArg(python_op, key="another_key")
      assert actual.key == "another_key"
      actual_new_key = actual["another_key_2"]
      assert actual_new_key.key == "another_key_2"
  
imports: from __future__ import annotations
  import pytest
  from airflow.models.xcom_arg import XComArg
  from airflow.operators.bash import BashOperator
  from airflow.operators.python import PythonOperator
  from airflow.utils.types import NOTSET
  from tests.test_utils.config import conf_vars
  from tests.test_utils.db import clear_db_dags, clear_db_runs
label_desc: Use image node_id 7 for calling the TestXComArgBuild obj's underlying member method code with example usage: obj.test_xcom_key_getitem(dag_maker) without return types