code: def test_registered():
      assert "ws" in backends
      backend = get_backend("ws")
      assert isinstance(backend, ws.WSBackend)
  
file_path: distributed/distributed/comm/tests/test_ws.py
imports: from __future__ import annotations
  import asyncio
  import os
  import random
  import warnings
  import pytest
  import dask
  from distributed import Client, Scheduler, Worker
  from distributed.comm import connect, listen, ws
  from distributed.comm.core import FatalCommClosedError
  from distributed.comm.registry import backends, get_backend
  from distributed.comm.tests.test_comms import check_tls_extra
  from distributed.security import Security
  from distributed.utils_test import gen_cluster, gen_test, get_client_ssl_context, get_server_ssl_context, inc, xfail_ssl_issue5601
label_desc: Use image node_id 1 for calling a global function with example usage: test_registered() without return types