I would work on improving some software that I’ve already started that makes heavy use of JavaScript and third party services. While I’ve gone back and forth on the TDD bandwagon I’ve always believed that testing code helps improve reliability and leads to a better design.
I’ve used some of the tools in the book in the past but older versions. So I know I’m missing out on some of the new Rspec3 goodness, and some of the things it always did like custom matchers that I never was able to get working.