Add Unit testing

Currently the project has been hacked together.

Let's get some unit testing in place for easier refactoring.

Likely this will require some refactoring before being feasible, too.

No files, tests, or entry points are named. Start by surveying the project structure and existing build setup, then determine the unit-testing framework and which refactoring is required before tests are feasible. Done means a documented, runnable unit-test setup with meaningful coverage for an agreed scope.

Written by the indexing model from the issue text.