code: def test_get_gcs_client_without_gcs_credential_name(self):
      mock = MagicMock()
      os.environ["env_name"] = ""
      with patch("luigi.contrib.gcs.GCSClient", mock):
          GCSConfig(gcs_credential_name="env_name")._get_gcs_client()
          self.assertEqual(
              dict(oauth_credentials=None), mock.call_args[1]
          )
  
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 1 for calling the TestGCSConfig obj's underlying member method code with example usage: obj.test_get_gcs_client_without_gcs_credential_name() without return types