The RSpec Book: Behaviour-Driven Development with Rspec, Cucumber, and Friends

You'll get started right away with RSpec 2 and Cucumber by developing a simple game, using Cucumber to express high-level requirements in language your customer understands, and RSpec to express more granular requirements that focus on the behavior of individual objects in the system. You'll learn how to use test doubles (mocks and stubs) to control the environment and focus the RSpec examples on one object at a time, and how to customize RSpec to "speak" in the language of your domain.
You'll develop Rails 3 applications and use companion tools such as Webrat and Selenium to express requirements for web applications both in memory and in the browser. And you'll learn to specify Rails views, controllers, and models, each in complete isolation from the other.
Whether you're developing applications, frameworks, or the libraries that power them, The RSpec Book will help you write better code, better tests, and deliver better software to happier users.