我很难嘲笑redis createClient() nodejs中使用mocha和sinon的方法。这是我的index.js的一个片段。在socket类中，有一个create redis连接。现在在我的单元测试中，我遇到了这个错误 TypeError: Cannot stub non-existent property createClient . 我好像不明白为什么？是因为嘲弄的命令吗？

const express = require("express");
const http = require('http');
const redis = require('redis');
const expressApp = express();
const server = http.createServer(expressApp);
const io = require('socket.io')(server, {
    pingInterval: 10000,
    pingTimeout: 5000
});
const config = require('config');
const log = require('gelf-pro');
const HTTP_PORT = 3000;

// Socket IO call backs
io.on("connection", (client) => {    
    new Socket(client);
});

// export the server so it can be easily called for testing
exports.server = server.listen(HTTP_PORT, () => {
    log.info('socketio server started at port ' + HTTP_PORT);
});

单元测试代码：

'use strict'

var expect = require('chai').expect
  , redis = require('redis')
  , redisMock = require('redis-mock')
  , sinon = require('sinon')
  , io = require('socket.io-client')
  , ioOptions = { 
      transports: ['websocket']
    , forceNew: true
    , reconnection: false
  }
  , testMsg = JSON.stringify({message: 'HelloWorld'})
  , sender
  , receiver

describe('Chat Events', function(){
  beforeEach(function(done){

    sinon
      .stub(redis.RedisClient.prototype, 'createClient')
      .callsFake(function() {
        console.log('mock redis called');
        return redisMock.createClient();
      });

    // connect two io clients
    sender = io('http://localhost:3000/', ioOptions)
    receiver = io('http://localhost:3000/', ioOptions)

    // finish beforeEach setup
    done()
  })
  afterEach(function(done){

    // disconnect io clients after each test
    sender.disconnect()
    receiver.disconnect()
    done()
  })

  describe('Message Events', function(){
    it('Clients should receive a message when the `message` event is emited.', function(done){
      sender.emit('message', testMsg)
      receiver.on('ackmessage', function(msg){
        expect(msg).to.contains(testMsg)
        done()
      })
    })
  })
})