code: def test_one_worker(self):
      self.add_master()
      self.add_worker(n_cpu=1)
      cluster_monitor = ClusterMonitor("localhost:{}".format(self.port))
      time.sleep(30)
      self.assertEqual(1, len(cluster_monitor.data["workers"]))
      self.remove_all_workers()
      time.sleep(40)
      self.assertEqual(0, len(cluster_monitor.data["workers"]))
  
imports: import unittest
  import parl
  from parl.remote.monitor import ClusterMonitor
  import time
  import threading
  from parl.remote import exceptions
  import subprocess
  from parl.utils.test_utils import XparlTestCase
label_desc: Use image node_id 1 for calling the TestClusterMonitor obj's underlying member method code with example usage: obj.test_one_worker() without return types