Assert Valid Asset is a plugin to validate your (X)HTML and CSS using the W3C Validator web service and the W3C CSS Validation Service as part of your functional or unit tests. The CSS and HTML fragments are cached in $RAILS_ROOT/tmp/test/assets as are the results from the web service. This means that your tests will not be slowed down unless the output has changed. For more information and usage examples, see the plugin README.
Author: Peter Donald
Installation:
ruby script/plugin install http://www.realityforge.org/svn/code/assert-valid-asset/trunk/