code: def test_index(ManagedServerLoop: MSL) -> None:
      application = Application()
      with ManagedServerLoop(application) as server:
          assert server._tornado.index is None
  
      with ManagedServerLoop(application, index="foo") as server:
          assert server._tornado.index == "foo"
  
imports: from __future__ import annotations
  import pytest
  import json
  import logging
  from _util_server import http_get, url
  from tornado.web import StaticFileHandler
  from bokeh.application import Application
  from bokeh.client import pull_session
  from bokeh.core.types import ID
  from bokeh.server.auth_provider import NullAuth
  from bokeh.server.views.static_handler import StaticHandler
  from bokeh.server.views.ws import WSHandler
  from tests.support.plugins.managed_server_loop import MSL
  from tests.support.util.env import envset
  import bokeh.server.tornado
label_desc: Use image node_id 4 for calling a global function with example usage: test_index(ManagedServerLoop) without return types