Rails: LoadError: cannot load such file -- active_resource/railtie

Issue when upgrading from Rails 3.2 to Rails 4.0, having run bundle update rails ... to update Rails and other gems with conflating gems, running bundle exec rake spec throws the following error:

Copyrake aborted!
LoadError: cannot load such file -- active_resource/railtie
/vagrant/config/application.rb:7:in `require'
/vagrant/config/application.rb:7:in `<top (required)>'
/vagrant/Rakefile:4:in `require'
/vagrant/Rakefile:4:in `<top (required)>'
(See full trace by running task with --trace)

Solution

ActiveResource is no longer an integral part of Rails and has been moved to a separate gem. If you don't require ActiveResource in your app then remove require "active_resource/railtie" from the file in question (application.rb in this case)