As a test-first developer working through this material I threw the tests together as I went through with mocha and chai.
Run with:
npm install
npm test
It might be helpful to use this test framework instead of the one that comes with the book if you want to just see a single solution at a time instead of spoilers for all the solutions for a chapter (at least I wanted that ;).
Sometimes my solutions vary slightly from those of the author, but the book's exercises are tightly written, leaving few options but what he's looking for.
Enjoy!