Spork is a great gem that runs a distributed Ruby server which you can run your tests against. The benefit of using a DRb server is that you don’t have to wait for Rails to boot up every time you want to run your RSpec and Cucumber tests, which means doing test or behavior driven development with these testing frameworks in Rails is actually possible because you can avoid the 30+ second boot times that often accompany large Rails applications. Generally to make Spork useful you need to not cache your classes in your testing environment by adding the following line to environments/test.rb:

config.cache_classes = false

The reason for this is that you want spork to re-load the related classes one every test-run, so that changes that you make to your classes are re-loaded rather than using a cached version from when Spork first booted. The downside of this approach is that you lose the cached class performance boost to your tests when you are running outside of the DRb server, for example in your continuous integration environment. To remedy this simply change the configuration line to:

config.cache_classes = ENV['DRB'] == 'true' ? false : true

Spork sets the ENV['DRB'] variable to true when it is booted, so this line lets you conditionally cache classes depending on if you are running in the spork distributed ruby environment. Happy testing!

UPDATE (June 1, 2011): I’ve written a more complete post on cached-classes, spork, sham and Rspec, which includes a gist of the complete spec_helper.rb file, test.rb file and Gemfile.