The game in question is the Atlantis: The Second Age roleplaying game, published by Khepera Publishing. The playtesting involves testing out some new, basic modifications to the way in which beasties work in combat, though I can't talk about this very much for obvious reasons.
Once the players arrived at my place and we got things off to a good start by going over the game mechanics of the Atlantis system once more, the players got into the playtest. As player characters, they used their own player characters that they've created (though these still need to be slightly revised to the modified rules in the Khepera edition of the game, but that will wait until I have my physical copy of the game, if it ever shows up) as well as several new ones that the group of players rolled up to test the mechanics of the game and get a better feel for things.
I created several new stat blocks for creatures for the evening, including two beasties I've been meaning to do up for the current set-up for Atlantis, and used these as well as some of the creatures and beasties and two-legged foes that the players had taken on when they did the first playtest session (you can read that blog entry here).
The players were, once again, pretty pleased with how combat went, liked the new rules even more than they did with the first playtest session, and found themselves feeling more comfortable with the Atlantis: The Second Age game mechanics and combat system.
As I mentioned in the previous post about this, I have no idea whether these changes will be implemented in a future supplement for the Atlantis game or not, but I sure hope so. :)
Once more, a fun night was had by the players (the relative "newbies" Angela and David telling me they like this playtesting thing), and once again the players commented quite strongly about the fact that it makes them want to play Atlantis: The Second Age even more!
Can't wait until my physical copy of the book gets here! (Soon, I hope!)