code: def db_cluster_id(rds_hook: RdsHook) -> str:
      """Creates an RDS DB cluster and returns its id"""
      response = rds_hook.conn.create_db_cluster(
          DBClusterIdentifier="testrdshook-db-cluster",
          Engine="postgres",
          MasterUsername="testrdshook",
          MasterUserPassword="testrdshook",
          DBClusterInstanceClass="db.t4g.micro",
          AllocatedStorage=20,
      )
      return response["DBCluster"]["DBClusterIdentifier"]
  
imports: from __future__ import annotations
  from typing import TYPE_CHECKING, Generator
  from unittest.mock import patch
  import pytest
  from moto import mock_rds
  from airflow.exceptions import AirflowException, AirflowNotFoundException
  from airflow.providers.amazon.aws.hooks.rds import RdsHook
label_desc: Use image node_id 3 for calling a global function with example usage: db_cluster_id(rds_hook) and returns: response