How easy would it be to make COVID tests test for Histamines?

My in-laws have tested positive for 'COVID' and their symptoms are allergy symptoms. I currently have bad allergies as I do this time every year and an anti-histamine makes me feel better.

I suspect that COVID tests are testing for Histamines. It would be the easiest way to fake a pandemic. It's basically slight of hand or a magicians trick.