How can I detect if my express (4.0) node.js app is using a specific piece middleware?

For the purposes of Unit testing I'd like to be able to work out if some middleware is in use.

For example

app.js

var express = require('express');
var morgan = require('morgan');

module.exports = function(options) {
    var app = express();

    if (options.logRequests) {
        app.use(morgan('dev'));
    }

    return app;
}

app.test.js (run via mocha)

describe('app', function(){
    it('should log requests when initialized with the `log requests` option', function() {
        var app = require('./app)({ logRequests: true });

        // Something to establish whether or not morgan is in use
    })
})

I believe middleware is pushed to the seemingly undocumented express "stack", which can be accessed via the app._router.stack array, but this looks like a pretty horrible way to get to what I'm after.

Is anyone aware of a better way to this my assertion?

Thanks