code: def test_defer_mode(self, _, defer_method):
      op = BigQueryDataTransferServiceStartTransferRunsOperator(
          transfer_config_id=TRANSFER_CONFIG_ID,
          task_id="id",
          project_id=PROJECT_ID,
          deferrable=True,
      )
      ti = mock.MagicMock()
  
      op.execute({"ti": ti})
  
      defer_method.assert_called_once()
  
file_path: airflow/tests/providers/google/cloud/operators/test_bigquery_dts.py
imports: from __future__ import annotations
  from unittest import mock
  from google.api_core.gapic_v1.method import DEFAULT
  from google.cloud.bigquery_datatransfer_v1 import StartManualTransferRunsResponse, TransferConfig, TransferRun
  from airflow.providers.google.cloud.operators.bigquery_dts import BigQueryCreateDataTransferOperator, BigQueryDataTransferServiceStartTransferRunsOperator, BigQueryDeleteDataTransferConfigOperator
label_desc: Use image node_id 2 for calling the TestBigQueryDataTransferServiceStartTransferRunsOperator obj's underlying member method code with example usage: obj.test_defer_mode(_, defer_method) without return types