- Joined
- Feb 6, 2010
- Messages
- 1,429
Attention ladies and gentlemen be ready to shout "The Cake Is A Lie" At the top of your lungs

I found the cake! It's not a lie!
Yes, the writing was of a previous test subject who, presumably, made it all the way to GLaDOS and died (His/her hints are everywhere). They most likely assumed that saying you will get cake was one of GLaDOS's lies to try and trick you to continuing with the tests.
[Edit]
This is all speculation, it could have been an Aperture Science employee, but I think it's a test subject because they were very upset about killing the companion cube.