As has been alluded to, gravity is an extremely weak force, so any gravitational effect is easily masked by electroweak forces until you accumulate a very significant mass. There's no way they can measure this on a single atom.
But easy to test with 2 atoms! Smash them together at a high enough speed where e=mc^2 says they would create a black hole. If they are destroyed in a blip of Hawking radiation, they had gravity!
Doesn't sound like it would work.
I'm not sure it's easy to distinguish the Hawking radiation from the stuff that comes out otherwise. I guess the Hawking radiation should be thermal but for a borderline small black hole there will be few particles.