Test coverage!

[danielbachhuber]

It would be great if this project included test coverage, both to ensure the quality of the codebase and for others to learn from.

If you're looking for prior art to copy from, https://github.com/runcommand/runcommand-theme has a test suite that performs shallow rendering of React components using Mocha, Chai, Enzyme and Chai + Enzyme.

One challenge is that, in addition to testing UI interactions, you'll also want to test API interactions. I haven't come up with a good, easy to use way of mocking WP-API in a JS test suite yet, so I'd be curious to hear your thoughts.