And one is none. Our buddy Turk had the slide on his 10mm Witness crack the other day. Like Tam sez, guns break. Even tested designs like the Witness (which is essentially a CZ-75 clone) will break, because like anything else, they are a machine and prone to mechanical failures, failures during the manufacturing process, etc.
Luckily, spare parts for Witness pistols are readily available, so Turk shouldn’t have too much trouble getting his gun back up and running.