Okay, you’ve tested the design/front-end of your site and now you are ready to put the site on your staging server. Test it again. Make a hard and fast rule to always test every time you make any change to your site just to be sure you haven’t accidentally introduced an error.
Other steps you should take during the testing stage include asking other people to test your website and to proofread the text. You and your staff are just too close to the project to notice what would otherwise be embarrassing errors.
If you developed a site that exists simultaneously in different formatted versions — flash/HTML, frame/non-frame — then, depending on the browser, you must test every version with every browser and with all of the possible option settings.