Write Unit Tests to cover functionality

I'm not an expert at TS / JS so I don't know if it'll be possible to fully unit test all the functionality for the package. But we do need a safety net for changes coming in and new versions going out.

This issue is a reminder that we need unit tests for the package.

No files, tests, or entry points are named. Start by mapping the package's functionality and test setup, then define a scoped coverage plan; done means the agreed unit tests provide a safety net for the package's supported behavior.

Written by the indexing model from the issue text.