Unit tests

NodeJS native `asserts` library should be enough:
http://nodejs.org/docs/latest/api/assert.html

but research shows [mocha](https://github.com/visionmedia/mocha) is also popular:
http://webapplog.com/test-driven-development-in-node-js-with-mocha/
http://niallohiggins.com/2012/03/28/3-quick-tips-for-writing-tests-in-nodejs/