Some questions to answer regarding js tests:
My initial thoughts were:
Hey Andrew, sounds good!
I'll throw together a pull request on https://github.com/ankane/chartkick.js with some basic outline tests + docs.
I'm going to assume that the js in the gem is updated from https://github.com/ankane/chartkick.js ? Is this done automatically or manually?
Correct. It's done manually on new releases of chartkick.js, and occasionally in between releases when it'll benefit someone.