code: def test_single_rank_failure(self, mock_get_min_start_hosts):
      for exit_mode in ["exception", "kill"]:
          discovery_schedule = [
              (None, ["localhost:2", "127.0.0.1:2"]),
          ]
  
          exit_schedule = {
              str((1, 0)): [0],
          }
  
          results = self._run(
              discovery_schedule,
              exit_schedule=exit_schedule,
              exit_mode=exit_mode,
          )
  
          self.assertEqual(len(results), 3)
  
          self.assertEqual(results[0]["start_rank"], 0)
          self.assertEqual(results[0]["size"], 4)
          self.assertEqual(results[0]["rendezvous"], 1)
  
          self.assertEqual(results[1]["start_rank"], 2)
          self.assertEqual(results[1]["size"], 2)
          self.assertEqual(results[1]["rendezvous"], 2)
  
          self.assertEqual(results[2]["start_rank"], 2)
          self.assertEqual(results[2]["size"], 2)
          self.assertEqual(results[2]["rendezvous"], 2)
  
imports: import contextlib
  import json
  import os
  import sys
  from typing import Callable
  import mock
  import pytest
  from horovod.runner.common.util import config_parser
  from horovod.runner.elastic import constants
  from horovod.runner.launch import parse_args, _run_elastic
  from common import override_args, temppath
label_desc: Use image node_id 4 for calling the BaseElasticTests obj's underlying member method code with example usage: obj.test_single_rank_failure(mock_get_min_start_hosts) without return types