Testing Express.js res.render within promise with Mocha & Sinon spy

Following a similar pattern to this example I've been attempting to test my routes in an Express.js application but I'm unable to get my spy to verify that res.render has been called when wrapped in a promise.then.

Here's a simplified example where'd I expect calledOnce to be true but it's returning false.

Code under test:

var model = {
  get: function() {
    return new Promise(function(res, rej) {
      return res('success');
    });
  }
};

module.exports = function (req, res) {
  model.get().then(function (data) {
    res.render('home', data);
  }).catch(function (err) {
    console.log(err);
  });
};

Test:

var expect = require('chai').expect;
var sinon = require('sinon');
var home = require('./home');

describe('home route', function() {
  it('should return a rendered response', function() {
    var req = {};

    var res = {
      render: sinon.spy()
    };

    home(req, res);

    expect(res.render.calledOnce).to.be.true;
  });
});