code: def test_allowed_message_origins_dev_mode(self):
      response = self.fetch("/_stcore/host-config")
      self.assertEqual(200, response.code)
      # Check that localhost has been appended/allowed in dev mode
      origins_list = json.loads(response.body)["allowedOrigins"]
      self.assertIn("http://localhost", origins_list)
  
imports: import json
  import os
  import tempfile
  from unittest.mock import MagicMock
  import tornado.httpserver
  import tornado.testing
  import tornado.web
  import tornado.websocket
  from streamlit.runtime.forward_msg_cache import ForwardMsgCache, populate_hash_if_needed
  from streamlit.runtime.runtime_util import serialize_forward_msg
  from streamlit.web.server.routes import _DEFAULT_ALLOWED_MESSAGE_ORIGINS
  from streamlit.web.server.server import HEALTH_ENDPOINT, HOST_CONFIG_ENDPOINT, MESSAGE_ENDPOINT, HealthHandler, HostConfigHandler, MessageCacheHandler, StaticFileHandler
  from tests.streamlit.message_mocks import create_dataframe_msg
  from tests.testutil import patch_config_options
label_desc: Use image node_id 4 for calling the HostConfigHandlerTest obj's underlying member method code with example usage: obj.test_allowed_message_origins_dev_mode() without return types