What worries me greatly is the utter negligence, not for the first time, by some pen-pusher at VOSA, because a belt that does not work is a potential killer, so for safety's sake it is ESSENTIAL that they are tested for correct operation. If it needs something special, such as tilting the car to activate a deceleration sensor, well a suitable test rig needs to be devised and incorporated into the test.
No other safety-critical industry would accept the situation where a vital item was untested, and it would never have been allowed to be fitted in the first place if its design made it untestable. The fact that we are debating this here, as intelligent adults, is an utter disgrace, because there should be nothing to discuss. Shame on you, VOSA, yet again....
Now can the sensible people here (which includes everyone in this debate so far) think up a good way of testing it properly, other than standing the car on its nose?