Have any tests been done to see what would happen if it collided with an airliner?
Not that I know of but an 11 gram mass is not going to do much to a jet traveling at 600+ mph.
But then again the odds of it happening are extremely, extremely rare. An aircraft hasn’t hit a balloon yet, AFAIK.
A few years ago I did read of an incident in which an amateur balloon did hit a car after the balloon burst and it descended down on its parachute. The payload landed on either a state highway or an interstate while the cars were traveling at highway speeds. IIRC, it did crack the windshield but did not go through it. The payload was about two or three pounds and the payload container was made out of Styrofoam.
The payload was recovered and the owner of the payload paid for the owner to have the glass replaced.