code: def test_get_gcs_client_with_file_path(self):
      mock = MagicMock()
      file_path = "test.json"
      os.environ["env_name"] = file_path
      with patch("luigi.contrib.gcs.GCSClient"):
          with patch(
              "google.oauth2.service_account.Credentials.from_service_account_file",
              mock,
          ):
              with patch("os.path.isfile", return_value=True):
                  GCSConfig(
                      gcs_credential_name="env_name"
                  )._get_gcs_client()
                  self.assertEqual(file_path, 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 2 for calling the TestGCSConfig obj's underlying member method code with example usage: obj.test_get_gcs_client_with_file_path() without return types