code: def test_begin_transaction(self, mock_get_conn):
      self.datastore_hook.connection = mock_get_conn.return_value
  
      transaction = self.datastore_hook.begin_transaction(
          project_id=GCP_PROJECT_ID,
          transaction_options={},
      )
  
      projects = self.datastore_hook.connection.projects
      projects.assert_called_once_with()
      begin_transaction = projects.return_value.beginTransaction
      begin_transaction.assert_called_once_with(
          projectId=GCP_PROJECT_ID, body={"transactionOptions": {}}
      )
      execute = begin_transaction.return_value.execute
      execute.assert_called_once_with(num_retries=mock.ANY)
      assert transaction == execute.return_value["transaction"]
  
imports: from __future__ import annotations
  from unittest import mock
  from unittest.mock import call, patch
  import pytest
  from airflow.exceptions import AirflowException
  from airflow.providers.google.cloud.hooks.datastore import DatastoreHook
label_desc: Use image node_id 6 for calling the TestDatastoreHook obj's underlying member method code with example usage: obj.test_begin_transaction(mock_get_conn) without return types