Project requires a unit test suite

[robberwick]

At some point soon, we should be thinking about providing some coverage for the existing code with a unit test suite. This will make code easier and quicker to refactor (or when merging PRs) by providing feedback as to any regressions or breakages introduced as a result of changes.

It doesn't have to be anything hugely fancy to begin with - just enough to make sure that prodding the code in one place doesn't break it in another. Once even a basic suite exists, it can be fleshed out later.