Create tests to ensure that all features work as expected

[adamghill]

I see a directory of examples in this repo which is great for manual testing, but it might be useful to have automated tests for the things that can be tested.

These UI frameworks seem to be a little bit challenging to test reliably, but Playwright might be an option -- it seems to be the least flaky end-to-end testing framework that I have used.

Other frameworks for unit testing the internal JavaScript abound. Personally, I've used ava and jest extensively, and have some experience with vitest. But, this feels like a subjective decision up to the maintainer -- they all basically work similarly as far as I'm concerned.