code: def test_execute_no_messages(self, mock_hook):
      operator = PubSubPullOperator(
          task_id=TASK_ID,
          project_id=TEST_PROJECT,
          subscription=TEST_SUBSCRIPTION,
      )
  
      mock_hook.return_value.pull.return_value = []
      assert [] == operator.execute({})
  
imports: from __future__ import annotations
  from typing import Any
  from unittest import mock
  from google.api_core.gapic_v1.method import DEFAULT
  from google.cloud.pubsub_v1.types import ReceivedMessage
  from airflow.providers.google.cloud.operators.pubsub import PubSubCreateSubscriptionOperator, PubSubCreateTopicOperator, PubSubDeleteSubscriptionOperator, PubSubDeleteTopicOperator, PubSubPublishMessageOperator, PubSubPullOperator
label_desc: Use image node_id 3 for calling the TestPubSubPullOperator obj's underlying member method code with example usage: obj.test_execute_no_messages(mock_hook) without return types