Mocking the Express.js response object

controller.js

module.exports = {
  test : function(req, res) {
    setTimeout(function() {
      res.send({ testing : true }, 200);
    }, 5000);
  },
}

index.js

var express = require('express')
  , app = exports = module.exports = express()
  , ctrl = require('./controller');

app.get('/', ctrl.test);

response.mock.js

var util = require('util')
  , events = require('events').EventEmitter;

var res = function () {
};

util.inherits(res, events);

res.prototype.send = function(payload, code) {
  this.emit('response', {
    code: code,
    response: payload
  });
}

module.exports = function() {
  return new res();
};

test.spec.js

var expect = require('chai').expect
  , res = require('./mocks/response')()
  , testing = require('./controller');

describe('Testing', function(){
  it('Should send an object with a testing key', function(done){
    res.on('response', function(resp) {
      expect(resp.response).to.have.property('testing');
      expect(resp.response.testing).to.equal(true);
      done();
    });
    
    testing.test({}, res);
  });
});