CSSunit is a project mainly written in ..., based on the GPL-3.0 license.
Unit Testing framework for CSS using JavaScript, jQuery and QUnit
We are not going to test how a page looks but only if DOM element or group of elements has the required style. But what does mean "required"?
Imagine, you finish the style of links or an home page. By exporting this element's styles and constantly checking that no other CSS rule overwrites them, you keep this work safe.
Now, if you know that an element needs to be at 30px from the border of the windows... you can also test that!
GPL V3 see LICENSE.txt or http://www.gnu.org/licenses/gpl-3.0.html