code: def test_process_exists(self):
      def fn():
          time.sleep(100000)
  
      mpr = multi_process_runner.MultiProcessRunner(
          fn, multi_worker_test_base.create_cluster_spec(num_workers=1)
      )
      mpr.start()
      self.assertTrue(mpr.process_exists("worker", 0))
      mpr.terminate("worker", 0)
      # Worker 0 should exit at some point, or else the test would time out.
      while mpr.process_exists("worker", 0):
          time.sleep(1)
  
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 25 for calling the MultiProcessRunnerTest obj's underlying member method code with example usage: obj.test_process_exists() without return types