code: def test_prepare_template(self):
      report = {"key": "value"}
      with NamedTemporaryFile("w+", suffix=".json") as f:
          f.write(json.dumps(report))
          f.flush()
          op = GoogleCampaignManagerInsertReportOperator(
              profile_id=PROFILE_ID,
              report=f.name,
              api_version=API_VERSION,
              task_id="test_task",
          )
          op.prepare_template()
  
      assert isinstance(op.report, dict)
      assert op.report == report
  
imports: from __future__ import annotations
  import json
  from tempfile import NamedTemporaryFile
  from unittest import mock
  import pytest
  from airflow.models import DAG, TaskInstance
  from airflow.providers.google.marketing_platform.operators.campaign_manager import GoogleCampaignManagerBatchInsertConversionsOperator, GoogleCampaignManagerBatchUpdateConversionsOperator, GoogleCampaignManagerDeleteReportOperator, GoogleCampaignManagerDownloadReportOperator, GoogleCampaignManagerInsertReportOperator, GoogleCampaignManagerRunReportOperator
  from airflow.utils import timezone
  from airflow.utils.session import create_session
label_desc: Use image node_id 2 for calling the TestGoogleCampaignManagerInsertReportOperator obj's underlying member method code with example usage: obj.test_prepare_template() without return types