I put a simplified version in the article to make it simple, but the macro I actually use in my games is slightly more advanced, and will output more informations about the error and its context.
Ah, right! - my first version was just the assert, and it was working fine until one day I ended up on a wild goose chase because I was certain it had to be GL_INVALID_OPERATION. But in fact... it was GL_INVALID_ENUM :) So I just thought I'd save somebody a couple of minutes.
