code: def test_get_gcs_client_with_json(self):
      mock = MagicMock()
      json_str = '{"test": 1}'
      os.environ["env_name"] = json_str
      with patch("luigi.contrib.gcs.GCSClient"):
          with patch(
              "google.oauth2.service_account.Credentials.from_service_account_info",
              mock,
          ):
              GCSConfig(
                  gcs_credential_name="env_name"
              )._get_gcs_client()
              self.assertEqual(dict(test=1), mock.call_args[0][0])
  
file_path: gokart/test/test_gcs_config.py
imports: import os
  import unittest
  from unittest.mock import MagicMock, patch
  from gokart.gcs_config import GCSConfig
label_desc: Use image node_id 3 for calling the TestGCSConfig obj's underlying member method code with example usage: obj.test_get_gcs_client_with_json() without return types