Around 1990-1991 there was discussion in, I think, the RAeS about licensing TPs. Several test pilot prominente were involved, and I remember a slightly heated exchange on board the boat on which the cocktail party of the '91 SETP European symposium was held.
The end result is no licensing/accreditation system to embrace all test people. What do they say is the collective noun - a Disagreement of Test Pilots?