The TSA will take food you purchased inside the sterile, secure area and test it with their magic test strips. If you refuse, or they just don’t like your attitude, they’ll make sure you miss your flight.
But what does the TSA do right before they touch your food? They wipe their noses, perhaps spreading diseases to you. Nevermind that there are laws against intentionally infecting others with your bodily fluids. The TSA doesn’t care about laws.
In this short video clip, we see a TSA Officer, magic test strip in hand, wiping her disease-ridden nose before she’s about to touch a passenger’s food.
DISGUSTING.

This video show what appears to be a food court or dining area not the sterile area where a TSO would be doing the kind of tests.
This was in the sterile area. Nearly every airport has a food court in the sterile area. You can even see the test strip in her hand.