code: def test_ray_dask_basic(ray_start_1_cpu):
      @ray.remote
      def stringify(x):
          return "The answer is {}".format(x)
  
      zero_id = ray.put(0)
  
      def add(x, y):
          # Can retrieve ray objects from inside Dask.
          zero = ray.get(zero_id)
          # Can call Ray methods from inside Dask.
          return ray.get(stringify.remote(x + y + zero))
  
      add = dask.delayed(add)
  
      expected = "The answer is 6"
      # Test with explicit scheduler argument.
      assert add(2, 4).compute(scheduler=ray_dask_get) == expected
  
      # Test with config setter.
      enable_dask_on_ray()
      assert add(2, 4).compute() == expected
      disable_dask_on_ray()
  
      # Test with config setter as context manager.
      with enable_dask_on_ray():
          assert add(2, 4).compute() == expected
  
      # Test within Ray task.
  
      @ray.remote
      def call_add():
          z = add(2, 4)
          with ProgressBarCallback():
              r = z.compute(scheduler=ray_dask_get)
          return r
  
      ans = ray.get(call_add.remote())
      assert ans == "The answer is 6", ans
  
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 3 for calling a global function with example usage: test_ray_dask_basic(ray_start_1_cpu) and returns: str, ray, r