The only practical way to test a click-type torque wrench is against a beam-type. Beam types require no calibration.
Expecting a stem bolt on a bike from a LBS to be properly torqued is foolish, IMO. They are not that likely to have used torque wrench.
I've been wrenching on bikes for 25 years and using carbon parts for over 10 years. I've never used a torque wrench on any M5 or M6 bolt yet. Never had slippage problems or damaged anything yet.
If you can't manage to do a decent job of tightening these bolts without a torque wrench how are you ever going to make an adjustment out on the road? It pays to know what a moderate torque feel like, using a short handled hex wrench or a 4-5-6 Y-style wrench.