code: def teardown_class(cls):
      cls.loop.add_callback(
          lambda: tornado.ioloop.IOLoop.current().stop()
      )
      cls.loop.clear_current()
      cls.thread.join()
      cls.loop.close(all_fds=True)
  
imports: import queue
  import random
  import threading
  from functools import partial
  import tornado.ioloop
  from perspective import PerspectiveError, PerspectiveManager, Table
  from pytest import raises
label_desc: Use image node_id 2 for calling the TestAsync obj's underlying member method code with example usage: obj.teardown_class(cls) without return types