used to distribute patches/fixes that are still being tested, so not for everybody as in http://www.eset.com/support/news.php ".. An updated Anti-Stealth module (v1012, build date 20090526) is now available for testing purposes. To obtain it, open the ESET user interface, press the F5 key to open the Advanced Settings window, select Update in the left pane, then Advanced Update Setup in the right pane and check Enable Test Mode at the bottom of the window. The next time the client performs an virus signature database update, it will also download the updated Anti-Stealth module. If you are running ESET Smart Security, an updated Firewall module (v1047, build date 20090525) containing unrelated updates and fixes will also be downloaded for testing .."
Ronjor explains it at length here > https://www.wilderssecurity.com/showthread.php?t=242544&highlight=test mode