Add unit testing

[rodneybarnes]

Is your feature request related to a problem? Please describe.

There is currently no testing at all done with this website.

Describe the solution you'd like

It looks like Jest would be a good tool to use here:
https://jestjs.io/

Describe alternatives you've considered

Additional context

This would be a really interesting project for anyone keen on developing skills in best practices for web development.

It's something that should ideally have been incorporated into the initial workflow, but my lack of experience in this area would have prevented me from getting this website up at all had I tried to implement this.