Do you still need another tester?
Regarding my previous testing experiences, I took part in the Starcraft 2 and Diablo 3 betas, I was a tester for both Guild Wars and Guild Wars 2 and I tested many french Morrowind mods (including those which are probably still the best ones: the marvellous Serviteur de Ancetres and the huge Archipel de Pertevue, as well as countless quests mods, tweaks, gameplay mods etc.). Recently I also took part in the Dota2 beta test (during the very last months).
As for why I'd like to test the game, I'm a long time adventure lover (especially Lucasarts ones, but I was an ardent Sierra fan as well) and Loom was probably the one I liked the most, due to the sheer originality and the incredible atmosphere.