[V1] Add tests

[kriswep]

We need a sufficient enough test suite to be able to be confident about future refactors.

The test framework / runner needs to be discussed.

tape was mentioned, which is known to be a quite lightweight solution. However, in my opinion, adding things like mock suppport needs more configuration to work.

I also would like to add jest to the discussion, which is more a batteries included solution. Nice features are integrated snapshot testing (good for APIs), mocking and a quick interactive watch mode.

More opinions on test runners/framework welcome.

Also desirable would be some kind of CI setup, eg travis

[kriswep]

as a reference I added a first test suite implementation in #44.

[dereklieu]

Thanks @kriswep. Let's ticket out additional test coverage requests/to-dos separately.