Test them by placing a toothpick or cake tester in the center of the brownies. If it comes out with a few fudgy crumbs on it, it's ready! If it's just batter on the toothpick, continue baking them for a few more minutes. A clean toothpick in this case means they've baked too long. They'll still be tasty, but they won't have the same fudgy texture.