VGFacts

There is a way to get yourself stuck in a test chamber with no way to solve it. You have to try really hard to get the weighted storage cube on the other side of a door with no way of getting to it, or trapping yourself in a part of the map where you can't get out. However, once the developer figured out that the player could do this, they programed GLaDOS to deliver you a new cube and even gives you an achievement called "Like A Rat."

The easyest (and most known) are in test chamber 13:
https://www.youtube.com/watch?v=Ou2flCDU9Wg

and test chamber 15.
https://www.youtube.com/watch?v=I1sjThso5WE