You can perform four main types of testing on your site: unit, browser, performance, and user acceptance). At a minimum you want to conduct unit and browser tests on the visual design build before it gets added to a production system. This allows you to identify and fix any bugs before your users find them.
Unit testing happens during the build of the visual design elements. As you create your CSS, master pages, page layouts, and any other front-end development tasks, you should be checking the site constantly to make sure that what you are building matches the specific style-guide specifications that have been created. You can do these tests on the fly within your own development environment. In most cases, the results ...