code: def test_no_client_informative_error() -> None:
      with pytest.raises(ValueError, match="No global client found"):
          DaskStorage()
  
imports: from contextlib import contextmanager
  import time
  from typing import Iterator
  import numpy
  import pytest
  import optuna
  from optuna._imports import try_import
  from optuna.integration.dask import _OptunaSchedulerExtension
  from optuna.integration.dask import DaskStorage
  from optuna.testing.tempfile_pool import NamedTemporaryFilePool
  from optuna.trial import Trial
label_desc: Use image node_id 6 for calling a global function with example usage: test_no_client_informative_error() without return types