The intereting discussion about airspeed measurements seems fixed on pitot systems. However, several commercially available alternatives exist. Maybe they are too expensive or too new to be used by the civil aircraft industry. Some links to illustrate my statements.
Michigan Aerospace Corporation
Ophir Corporation Overview
Finally as far as I have found pitot tubes are normally tested in wind-tunnels and some water sprayed on them. However, the possible conditions seem not to cover the altitudes and velocities where many aircraft fly today.
Regards