sample_app_2nd_ed

I use exact gem versions because experience shows that even minor gem updates can break the tutorial. (RSpec is particularly guilty of this.) I generally recommend '~>' for more advanced users, but when getting your bearings I think it's best to use exact versions. That said, I keep the Rails Tutorial and sample application as up-to-date as possible—and in fact both have already been updated with the latest version. :-) http://ruby.railstutorial.org/ruby-on-rails-tutorial-book#se... $ gem install rails -v 3.2.12 https://github.com/railstutorial/sample_app_2nd_ed/blob/mast... gem 'rails', '3.2.12'

Run `git blame` on the code pathway that's throwing the exception (in the gem.) Look at the changes that have occurred on it and either move back to a version of the gem that works, or change my code to suit the new version. Alternatively, look at the changelog or just manually decrement the version number until my tests pass, obviously taking care not to move back past any critical security updates. Also, the precise version numbers used in railstutorial are available in the code listings here: https://github.com/railstutorial/sample_app_2nd_ed/blob/mast... The (fast paced|aglie|slapdash) nature of the rails ecosystem does necessitate a certain degree of attention to detail when it comes to versioning. However this applies equally to sinatra. It's worse with node.