超级测试测试表达中间件

找到了以下关于如何在express中测试中间件的提示:
https://github.com/visionmedia/express/blob/master/test/req.xhr.js
我想知道为什么我的考试总是通过。直到我注意到,当我从express复制测试时,他们的行为是一样的。我试着把他们搞砸,但他们一直在传球: https://github.com/visionmedia/express/blob/master/test/req.xhr.js

我在这里缺少什么?

it('should return true when X-Requested-With is xmlhttprequest', function(done){
  var app = express();

  app.use(function(req, res){
    req.xhr.should.be.false; //set to false, to fail the test but it still passes
    res.end();
  });

  request(app)
  .get('/')
  .set('X-Requested-With', 'xmlhttprequest')
  .end(function(res){
    done();
  })
})