Add tests

![http://media.tumblr.com/tumblr_m7or5ecmr41rter4a.gif](http://media.tumblr.com/tumblr_m7or5ecmr41rter4a.gif)

This project doesn't have any tests, so we should remedy that.
Was about to try that, but strictly experimentally.  I don't know if `incuna-mail` supports Python 3 yet and if it fails we'll have to make a separate issue for supporting it.