code: def list_blobs(self) -> Iterator["MockBlob"]:
      for blob_name in _MOCK_BUCKET_CONTENT.keys():
          yield MockBlob(blob_name)
  
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 4 for calling the MockBucket obj's underlying member method code with example usage: obj.list_blobs() without return types