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
  
file_path: fiber/tests/test_managers.py
imports: import fiber
  import time
  import pytest
  import docker
  from fiber.managers import AsyncManager
label_desc: Use image node_id 1 for calling the TestManagers obj's underlying member method code with example usage: obj.check_leak(request, client) without return types