Have you ever needed to see what a theme looks like with your content but you did not want to have to recreate your whole site on a testing server and import all your data? Well, Theme Test Drive to the rescue.
You simply download the plugin, unzip it, upload it to your WordPress install, install the plugin and then select the theme you want to test. This will allow you to go through your site as if it were live and see how it looks and works.
Now, have you ever need to make some changes to your current theme but did not want to shut down your site and you did not want your visitors to see a busted site? Well, Theme Test Drive to the rescue again.
Follow the steps above, but instead of installing a new theme, just duplicate your current theme via your ftp of choice. Once you have the duplicate theme, go into the dup and make a change to the style.css file and change the “Theme Name” – I just renamed the theme to have a 2 at the end of the name.
Reupload that style.css file and in the select menu under the Design -> Theme Test Drive page select your newly named theme and click enable at the bottom.
After that, just work off of the duplicate theme till you have everything looking the way you want and just either copy over all the changes to the old theme folder or change your default theme to the duplicate.
Complete install instructions, support and download can be found on the plugins site.