The Bastards Book of Ruby
This page covers the following topics related to Ruby : The Fundamentals, Installation, Tweet Fetching, Style, Conventions, and Debugging, Numbers, Strings, Variables, Methods, RubyGems, If and Else, Loops, Collections, Enumerables, File input/output, Reviewing Tweet Fetching, Supplementals, Design and Theory, The Projects.
Author(s): ruby.bastardsbook.com
NA Pages 
This book is the only Rails book that does test-driven development the entire time, an approach highly recommended by the experts but which has never been so clearly demonstrated before. Finally, by including Git, GitHub, and Heroku in the demo examples, the author really gives you a feel for what it’s like to do a real-world project. The tutorial’s code examples are not in isolation.
Author(s): Michael Hartl
NA Pages
Cookin' with Ruby on Rails Designing for Testability
This tutorial is intended for use with Rails 1.2.6.It has not yet been updated to support Rails 2.x.
Author(s): Bill Walton
NA Pages
