All depends on what type of window design it is. They do test them by shooting a dead chicken at them though! They aren't frozen like most people assume from watching Myth Busters.
Really PPG have been making windows for years and does a good job at it. But like any manufacturing plant making anything else, there are always screw ups, both employees, and windows that need fixed from time to time. Thing is the screw up employees never get fixed and there is a lot of them. They don't care if the window is good or bad. All in all though, the windows are inspected many times throughout the assembly process. Things do slip by though...
