Add automated testing

[jensren]

Testing is important for any software project, and it's easier to set up tests early in the project. Automated testing will also make our project easier to review, refactor, and maintain.

Current State

• Babel Jest is installed
• We have some files that seem like tests, but these files are all demos and not real tests

Goals for this Epic

• All components have unit tests, unless there is a good reason not to
• Unit tests are written in Jest
• Update documentation to reflect that this project now requires tests. Developers with no jest experience can find some linked tutorials/articles
• PR template reflects that this project now requires tests