Your marketing pitch is excellent and hit right at how I would have described my pain point with my knowledge of React 4 months ago. It still speaks to me and I feel an urge to give you money.

I have one problem though:

Why do you only introduce unit tests in part 12 out of 13? When I "Imagine how quickly I can get all of your work done with the right tools and best practices", it involves me being able to write solid automated tests for everything. Not only that, but if you introduce the proper way to set up testing early and carry it through the rest of the book, it helps the student keep themselves on track. When they get stuck, having a failing test helps them focus and have a clearer idea of how to move forward.

I strenuously urge you to introduce testing earlier.