Add unit tests for custom scripts

[blimmer]

There's currently a decent integration test framework to make sure the jest cache is restored properly. However, with #18, there were some additional inline scripts added. It would be nice to add unit tests for their behavior.

In the past, for private orbs I've written for clients, I've done this with a little script to extract the script content to .sh files and then use bats to test the files. That would be a nice addition to this repo.