Can you solve the MAGNET RIDDLE? ft YouTube CEO Susan Wojcicki

You can do the same with shavings. Create some shavings from each bar, if it sticks to the bar it came off of, the bar was magnetic to begin with, if it doesn't, the bar wasn't magnetic. You said it was a diamond file right ?

Second would be to repeatedly hit one with the hammer to see if it demagnetizes(thus proving it was the magnet), if not move onto the other one. Even without the hammer, you can just whip it onto the ground to achieve the same thing.