code: def test_nested_pool(self):
      def fn():
          # This runs in sub processes, so they are each using their own
          # MultiProcessPoolRunner.
          _global_pool.run(fn_that_does_nothing)
  
      _global_pool.run(fn)
  
imports: import ctypes
  import json
  import os
  import sys
  import threading
  import time
  import unittest
  from absl import logging
  from absl.testing import parameterized
  from tensorflow.python.distribute import combinations
  from tensorflow.python.distribute import multi_process_runner
  from tensorflow.python.distribute import multi_worker_test_base
  from tensorflow.python.eager import context
  from tensorflow.python.eager import test
label_desc: Use image node_id 7 for calling the MultiProcessPoolRunnerTest obj's underlying member method code with example usage: obj.test_nested_pool() without return types