Structuring Express Applications for Readability, Unit Testability: Promise Behavior; Tie Routes to Promise States; Test Promise Resolutions

app.js

//Tie Routes to Promise States

var middleware = require('./middleware.js');

app.get('example/uri', function(req, res, next) {
  middleware(req, res)
    .then(function() { next(); })
    .catch(res.json)
    .done();
});

middleware.js

//Promise Behavior

var Q = require('q');

module.exports = function(req, res) {
  var deferred = Q.defer();

  // Define middleware behavior and resolve or reject promises accordingly.
  
  return deferred.promise;
};

middlewareSpec.js

//Test Promise Resolutions
var httpMocks = require('node-mocks-http'),
    chai = require('chai'),
    chaiAsPromised = require('chai-as-promised');

chai.use(chaiAsPromised);

var middleware = require('path/to/middleware');

var req, res;

beforeEach(function (done) {
  req = httpMocks.createRequest(),
  res = httpMocks.createResponse();
});

describe('middleware', function() {
  it ('resolves under condition X with result Y', function () {
    return expect(middleware(req, res)).to.be.fulfilled.then(function() {
      // Assert
    });
  });
  
  it ('rejects under condition X with error Y', function () {
    return expect(middleware(req, res)).to.be.rejectedWith('Error String');
  });
});