Automated testing - disabling a GPS antenna
Maybe with an RF switch that works in the 1.5GHz range:

https://www.minicircuits.com/WebStore/Switches.html

They do have switches available, Look for RF 1.5GHz switch SPDT. They are expensive. You'll take a attenuation hit so it won't be the same as having an antenna. 

It may be simple enough to short it out with some kind of jumper, I'm not sure how much putting something like a 0.1" header on a 50Ω or 75Ω would distort the transmission line. I was thinking you would put it between signal and return not in series with the signal line.