code: def test_ray_dask_persist(ray_start_1_cpu):
      arr = da.ones(5) + 2
      result = arr.persist(scheduler=ray_dask_get)
      assert isinstance(
          next(iter(result.dask.values())),
          (ray.ObjectRef, ClientObjectRef),
      )
  
file_path: ray/python/ray/util/dask/tests/test_dask_scheduler.py
imports: import sys
  import unittest
  import dask
  import dask.array
  import dask.dataframe
  import numpy
  import pandas
  import pytest
  import ray
  from ray.tests.conftest import *
  from ray.util.client.common import ClientObjectRef
  from ray.util.dask import disable_dask_on_ray, enable_dask_on_ray, ray_dask_get
  from ray.util.dask.callbacks import ProgressBarCallback
label_desc: Use image node_id 5 for calling a global function with example usage: test_ray_dask_persist(ray_start_1_cpu) without return types