Real counterfeiters, go to the bank and get a $100 bundle of new uncirculated, dollars bills. Then they put the new bills in the dryer, with your funny money, aa few golf balls, and some poker chips, and run it on air dry for about an hour. This distributes the real ink from the new bills to your funny money, and roughs up your funny money enough that it doesn’t look fresh off the press.
This makes the tester pens, useless. Because the ink transferred from the ones reacts, the same as the ink on a real bill would.