It is useful to test code for the theme you just created on various browsers or platforms, as you may note that it may look right on IE but not on Firefox. Try IETester for IE browsers, but this is only for Windows. Find it at http://www.my-debugbar.com/wiki/IETester/HomePage

Some of the best sites to use for validating are www.validator.w3.org/ and http://xhtml-css.com/.

If you have been using PrestaShop 1.3.1 for development work, always test it on the other version to see compatibility. This will be useful for those who want to use your theme. More on validating in Chapter 8,Deploying Your New Themes.