code: def test_backend_simulator(self, time_mock: Mock) -> None:
      time_mock.return_value = 0.0
      dt = 0.001
      options = BackendSimulatorOptions(max_concurrency=2)
  
      # test init
      sim = BackendSimulator(options=options)
      self.assertEqual(sim.max_concurrency, 2)
      self.assertEqual(sim.time_scaling, 1.0)
      self.assertEqual(sim.failure_rate, 0.0)
      self.assertEqual(sim.num_queued, 0)
      self.assertEqual(sim.num_running, 0)
      self.assertEqual(sim.num_failed, 0)
      self.assertEqual(sim.num_completed, 0)
  
      # test run trial
      sim.run_trial(0, dt)
      self.assertEqual(sim.num_queued, 0)
      self.assertEqual(sim.num_running, 1)
      sim.run_trial(1, dt)
      self.assertEqual(sim.num_queued, 0)
      self.assertEqual(sim.num_running, 2)
      sim.run_trial(2, dt)
      self.assertEqual(sim.num_queued, 1)
      self.assertEqual(sim.num_running, 2)
      status = sim.status()
      self.assertEqual(status.queued, [2])
      self.assertEqual(status.running, [0, 1])
      self.assertEqual(status.failed, [])
      self.assertEqual(status.completed, [])
  
      # "Wait" some time
      time_mock.return_value += 1.5 * dt
      sim.update()
      self.assertEqual(sim.num_queued, 0)
      self.assertEqual(sim.num_running, 1)
      self.assertEqual(sim.num_failed, 0)
      self.assertEqual(sim.num_completed, 2)
  
      # extract state for later use
      state = sim.state()
  
      # let time pass and update
      time_mock.return_value += 10 * dt
      sim.update()
      self.assertEqual(sim.num_queued, 0)
      self.assertEqual(sim.num_running, 0)
      self.assertEqual(sim.num_failed, 0)
      self.assertEqual(sim.num_completed, 3)
  
      # test reset
      sim.max_concurrency = 3
      sim.time_scaling = 2.0
      sim.failure_rate, 0.5
      sim.reset()
      self.assertEqual(sim.max_concurrency, 2)
      self.assertEqual(sim.time_scaling, 1.0)
      self.assertEqual(sim.failure_rate, 0.0)
      self.assertEqual(sim.num_queued, 0)
      self.assertEqual(sim.num_running, 0)
      self.assertEqual(sim.num_failed, 0)
      self.assertEqual(sim.num_completed, 0)
  
      # test load state
      sim2 = BackendSimulator.from_state(state)
      self.assertEqual(sim2.max_concurrency, 2)
      self.assertEqual(sim2.time_scaling, 1.0)
      self.assertEqual(sim2.failure_rate, 0.0)
      self.assertEqual(sim2.num_queued, 0)
      self.assertEqual(sim2.num_running, 1)
      self.assertEqual(sim2.num_failed, 0)
      self.assertEqual(sim2.num_completed, 2)
      sim2.update()
      self.assertEqual(sim2.num_queued, 0)
      self.assertEqual(sim2.num_running, 0)
      self.assertEqual(sim2.num_failed, 0)
      self.assertEqual(sim2.num_completed, 3)
  
      # test failure rate
      options = BackendSimulatorOptions(
          max_concurrency=2, failure_rate=1.0
      )
      sim3 = BackendSimulator(options=options)
      sim3.run_trial(0, dt)
      self.assertEqual(sim3.num_queued, 0)
      self.assertEqual(sim3.num_running, 0)
      self.assertEqual(sim3.num_failed, 1)
      self.assertEqual(sim3.num_completed, 0)
  
imports: from unittest.mock import Mock, patch
  from ax.core.base_trial import TrialStatus
  from ax.utils.common.testutils import TestCase
  from ax.utils.testing.backend_simulator import BackendSimulator, BackendSimulatorOptions
label_desc: Use image node_id 1 for calling the BackendSimulatorTest obj's underlying member method code with example usage: obj.test_backend_simulator(time_mock) without return types