code: def test_messages_validation_negative(self, messages, error_message):
      with pytest.raises(PubSubException) as ctx:
          PubSubHook._validate_messages(messages)
      assert str(ctx.value) == error_message
  
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 33 for calling the TestPubSubHook obj's underlying member method code with example usage: obj.test_messages_validation_negative(messages, error_message) without return types