code: def test_disconnect():
      _client.disconnect()
  
      # release the port
      global _server
      _server.stdin.write("_close_\n")
      _server.stdin.flush()
      time.sleep(0.1)
      _server.terminate()
      _server = None
  
file_path: nni/test/ut/sdk/test_ws_channel.py
imports: import atexit
  from dataclasses import dataclass
  import importlib
  import json
  import os
  from pathlib import Path
  from subprocess import Popen, PIPE
  import sys
  import time
  from nni.runtime.command_channel.websocket import WsChannelClient
label_desc: Use image node_id 4 for calling a global function with example usage: test_disconnect() without return types