Manuel: thanks for posting here! (Errata turns out not to be a great place to have a back and forth discussion).
As I mentioned above, I personally prefer JQuery over Prototype. Yehuda prefers DataMapper over ActiveRecord. You prefer Cucumber over test/unit. At least one Rails core developer prefers rip over bundler. Any number of people prefer MySQL over SQLite. Many prefer haml over erb, sinatra over actionpack. Mercurial vs Git. The list goes on and on.
Each can make a solid case that what they are doing is “the state of the practice for doing the best”. An example of feedback I’ve gotten: “who in their right mind would develop and test with one database engine and then deploy with another?”
I need to have some overall plan over deciding what to cover and what not to cover. The plan I settled on was simple: if it is in the package of what you get when you
gem install rails, I cover it. If not, I leave it to part III.
Exceptions to that: I want to cover the concept of plugins, so I picked exactly one (will_paginate). The deployment chapter (which you should be seeing shortly) follows the recommendations of the Rails team, and further shows that the database can be replaced, and picks MySQL (undoubtedly much to the disappointment of PostgreSQL fans). I’m also not planning on covering ActiveResource in Part II in this edition, even though it clearly is a part of the base package, simply because I’m not convinced that it is something you have gotta know before you proceed.
But back to the topic at hand: I’m letting the Rails core team decide what is the state of the practice for doing the best, and focusing on covering what they select. Rails 3 is certainly a major upgrade, and they could have decided to rip test/unit out, make it a plugin for those that want it, and replace it with Cucumber/RSpec. And it is not too late: you are welcome to convince them to do so, and if they do, I will update the book to match. But meanwhile, my plan is to continue to track what they include.
Secondly, I will note that I barely scratch the surface of testing (or of active record or of any number of topics) in Part II. If you look closely, you will see that most of the new functionality isn’t getting a proper test. My goal with Part II is to introduce them to the concepts, with a minimum of repetition. There are a lot of concepts introduced in Part II, and if each were preceded by a test, that would greatly expand the book, and yet not manage to add much in the way of coverage of additional topics.
Finally, I will say that while I haven’t read it, I have taken a peek at Rails Test Prescriptions, and that might be just the book you are looking for. I’m going to try to get in contact with the author of that book and see if he has any suggestions.