Allows you to easily implement testing for a Rails engine.


Add test_engine as a development dependency to your gemspec

s.add_development_dependency 'test_engine'

If you are using Test::Unit then add the following to your Rakefile. This will define standard test tasks (test:units, test:functionals, test:integration):

require 'test_engine/test_unit'

Other test frameworks are not supported but this library is structured so that support can be easily added. I welcome patches.

By default your tests are run against the latest version of Rails installed on your machine. But if you wish to run against an earlier version, use the environment variable RAILS_VERSION

RAILS_VERSION=3.1.3 bundle exec rake test

If you need to include a library for your testing add it as a development dependency in your gemspec. For example if you need Capybara for your integration tests just add the following to your engine's gemspec.

s.add_development_dependency 'capybara'
s.add_development_dependency 'database_cleaner'

Only Rails 3 and greater is supported. This library assumes the tmp directory in your project is ok to stick temp files and you should have this directory ignored by your SCM.


To test your engine a dummy app is generated so your tests run in a real Rails environment. These dummy apps are re-used between test runs to keep things moving faster. If you need these dummy apps to be re-generated you can use this task to clean out the unwanted apps. This removes all dummy apps. If you just wish to remove a specific version you can use the RAILS_VERSION environment variable.

Bundler sudo prompt

Since a real Rails app is being generated bundler is being run on that app to ensure you have all the necessary dependencies. This means you may get a sudo prompt so the gems can be installed system-wide (just like as if you ran bundler manually on the app). If you do just enter the password and it will happily continue on.


If you want to see some real engines that use this library check out the following:

  • logmein - An engine for allowing users to login and logout.

  • remindme - An engine to allow a user to request a password reset, be sent a token link in e-mail which takes the user to a form so they can enter a new password.

Testing This Library

bundler exec rake test

Since the tests need to generate an old version of a Rails app you need a version of Rails >= 3.0 that is NOT the latest version installed.


The two main alternatives to this libary are:

  • Including a dummy app in the engine: We are actually doing this but instead of having you setup this manually and check it into your repo, this library is generating it at test time.

  • Faking a stripped down version of rails: This tries to avoid generating a full Rails app. A good example of this is While interesting, it seems very fragile (i.e. new versions of Rails could break easy) and since it isn't a normal Rails setup you might not have the same test results as you would have running it in a real app. I think this is where we should move to as generating an app is a crutch. But I think it should be something natively supported by Rails not hacked on.