I just found a bug in this nice plugin. The Test Drive works fine, but if i go with enabled test drive into the widget section, all widgets are removed from all sidebars, even in the real active theme. If you turn off the test drive, the widgets are still removed.
The second you go to the widget section, ALL visitors (even at access level 0 (admins only)) will see the default sidebar.
Theme Test Drive 2.8.1
Access Level: 0
Hope its getting fixed soon and thanks for this awesome plugin!