code: def test_upload_download(explicit_client: bool) -> None:
      with init_mock_client():
          bucket_name = "mock-bucket"
          if explicit_client:
              backend = GCSArtifactStore(
                  bucket_name, google.cloud.storage.Client()
              )
          else:
              backend = GCSArtifactStore(bucket_name)
  
          artifact_id = "dummy-uuid"
          dummy_content = b"Hello World"
          buf = io.BytesIO(dummy_content)
  
          backend.write(artifact_id, buf)
  
          client = google.cloud.storage.Client()
          assert len(list(client.bucket(bucket_name).list_blobs())) == 1
  
          blob = client.bucket(bucket_name).blob(artifact_id)
          assert blob.download_as_bytes() == dummy_content
  
          with backend.open_reader(artifact_id) as f:
              actual = f.read()
          assert actual == dummy_content
  
imports: from __future__ import annotations
  import contextlib
  import io
  import os
  from typing import Dict
  from typing import Optional
  from typing import TYPE_CHECKING
  from unittest.mock import patch
  import google.cloud.storage
  import pytest
  from optuna.artifacts import GCSArtifactStore
  from optuna.artifacts.exceptions import ArtifactNotFound
label_desc: Use image node_id 2 for calling a global function with example usage: test_upload_download(explicit_client) without return types