How to unit test express Router routes

I'm new to Node and Express and I'm trying to unit test my routes/controllers. I've separated my routes from my controllers. How do I go about testing my routes?

config/express.js

  var app = express();
  // middleware, etc
  var router = require('../app/router')(app);

app/router/index.js

  module.exports = function(app) {
    app.use('/api/books', require('./routes/books'));
  };

app/router/routes/books.js

  var controller = require('../../api/controllers/books');
  var express = require('express');
  var router = express.Router();

  router.get('/', controller.index);

  module.exports = router;

app/api/controllers/books.js

// this is just an example controller
exports.index = function(req, res) {
    return res.status(200).json('ok');
};

app/tests/api/routes/books.test.js

  var chai = require('chai');
  var should = chai.should();
  var sinon = require('sinon');

  describe('BookRoute', function() {

  });