code: def test_executor_is_serializable(backend):
      with backend(5) as executor:
          futures = [
              executor.submit(nested_jobs, executor) for _ in range(10)
          ]
          all_results = executor.wait(futures)
  
      assert sum(all_results) == 1000
  
imports: import os
  import time
  import pytest
  from orion.executor.base import AsyncException, ExecutorClosed, executor_factory
  from orion.executor.dask_backend import HAS_DASK, Dask
  from orion.executor.multiprocess_backend import PoolExecutor
  from orion.executor.ray_backend import HAS_RAY, Ray
  from orion.executor.single_backend import SingleExecutor
label_desc: Use image node_id 20 for calling a global function with example usage: test_executor_is_serializable(backend) without return types