In the first part we established why you should playtest your game, now I'll explain how to do it (or at least how I do it). Even though all of my games have been multiplayer games and I talk about playtest groups, there's no reason the same principles wouldn't apply to single player games and playtests. When When it comes to playtesting, there is really no such thing as 'too early'.
On playtesting, part 1
Hey, my name is Heikki and I've been helping the guys at SIEIDI in making Gunnheim the best game possible by arranging the formal playtest sessions for the game. I thought I'd shed some light on playtesting in general. My game design background is in tabletop games.