It is quite easy to extend your Ruby on Rails test infrastructure so every document is checked for validity.

1. Install the plugin assert_valid_markup.
2. Install my test_validation_helper.rb in your test directory.
3. Require the validation helper from your test/test_helper.rb:

   require File.expand_path(File.dirname(__FILE__) +
       "/test/test_validation_helper.rb")

After those three simple steps, your HTML and RSS documents are now being validated each time you run tests.

I am giving a brief presentation on this topic at the April 10, 2007 Boston Ruby Group meeting.

You can flip through a PDF of my slides if you would like more details.

Update: In addition to the PDF, my presentation is now hosted on slideshare and shown below. If you are reading this post in an aggregrator, you will need to click through for the show (or just use the PDF version).