Well there is a professional association that would seem to apply here, The Society of Experimental Test Pilots.
They grant membership based on experience, in several different grades from Associate upwards. All sorts of folks call themselves test pilots. I was on the Membership committee for a period in the late 1990s, and in general to be a full Member you really had to have done real test pilot work.
Now that being said, I think the French are the only country that issues a "Test Pilot" license.
Boeing has a long history of making their own Experimental Test Pilots, but recently have started to hire more graduates of ETPS, USAF TPS, EPNER and USN TPS.