That is one thing to note before you plan: Blizzard had originally set the test for October 19, but later changed it’s date to October 21. Players who are following older announcements or countdowns should take these into account.
The purpose of the event is to aid Blizzard in finding server issues prior to a worldwide release of the game. If you want to play, here is everything you need to know about the new schedule, Indian timings, how to install, what to do during the test and what becomes of your character in the end.