code: def test_create_subscription_failifexists(self, mock_service):
      mock_service.create_subscription.side_effect = AlreadyExists(
          f"Subscription already exists: {EXPANDED_SUBSCRIPTION}"
      )
      with pytest.raises(PubSubException) as ctx:
          self.pubsub_hook.create_subscription(
              project_id=TEST_PROJECT,
              topic=TEST_TOPIC,
              subscription=TEST_SUBSCRIPTION,
              fail_if_exists=True,
          )
      assert (
          str(ctx.value)
          == f"Subscription already exists: {EXPANDED_SUBSCRIPTION}"
      )
  
imports: from __future__ import annotations
  from unittest import mock
  from uuid import UUID
  import httplib2
  import pytest
  from google.api_core.exceptions import AlreadyExists, GoogleAPICallError
  from google.api_core.gapic_v1.method import DEFAULT
  from google.cloud.exceptions import NotFound
  from google.cloud.pubsub_v1.types import ReceivedMessage
  from googleapiclient.errors import HttpError
  from airflow.providers.google.cloud.hooks.pubsub import PubSubAsyncHook, PubSubException, PubSubHook
  from airflow.providers.google.common.consts import CLIENT_INFO
  from airflow.version import version
label_desc: Use image node_id 20 for calling the TestPubSubHook obj's underlying member method code with example usage: obj.test_create_subscription_failifexists(mock_service) without return types