code: def check_leak(self, request, client):
      assert fiber.active_children() == []
      if fiber.config.default_backend != "docker":
          yield
          return
      pre_workers = client.containers.list()
      yield
      post_workers = client.containers.list()
      assert pre_workers == post_workers
  
imports: import fiber
  import pickle
  import time
  import pytest
  import docker
  import collections
  import multiprocessing
  from fiber.queues import Pipe, SimpleQueue
  from fiber.socket import Socket
label_desc: Use image node_id 1 for calling the TestQueue obj's underlying member method code with example usage: obj.check_leak(request, client) without return types