code: def test_restart_workers(self):
      spec = self._get_worker_spec()
      agent = TestAgent(spec)
      worker_group = agent.get_worker_group()
  
      num_restarts = 3
      for _ in range(0, num_restarts):
          agent._restart_workers(worker_group)
          self.assertEqual(WorkerState.HEALTHY, worker_group.state)
  
          # test_rendezvous and test_initialize_workers
          # already validates the correctness of these fields
          # simply validate that they are not None
          # (e.g. that they get assigned)
          self.assertIsNotNone(worker_group.group_rank)
          self.assertIsNotNone(worker_group.group_world_size)
          for w in worker_group.workers:
              self.assertIsNotNone(w.id)
              self.assertIsNotNone(w.global_rank)
              self.assertIsNotNone(w.world_size)
  
      self.assertEqual(num_restarts, agent.start_workers_call_count)
      self.assertEqual(num_restarts, agent.stop_workers_call_count)
  
imports: import signal
  import unittest
  import uuid
  from typing import Any, Dict
  from unittest.mock import call, patch, MagicMock
  import torch.distributed.elastic.rendezvous.registry
  from torch.distributed.elastic.agent.server.api import RunResult, SimpleElasticAgent, WorkerGroup, WorkerSpec, WorkerState, _get_fq_hostname, _RoleInstanceInfo
  from torch.distributed.elastic.multiprocessing import SignalException
  from torch.distributed.elastic.multiprocessing.errors import ProcessFailure
  from torch.distributed.elastic.rendezvous import RendezvousHandler, RendezvousParameters
  from torch.distributed.elastic.utils.distributed import get_free_port
  from torch.testing._internal.common_utils import run_tests
label_desc: Use image node_id 16 for calling the SimpleElasticAgentTest obj's underlying member method code with example usage: obj.test_restart_workers() without return types