I know that radar cross section (RCS) tests were performed on geometric models of both the YF-22 and the YF-23 prototypes submitted for the Advanced Tactical Fighter (ATF) competition, but were the same tests performed on the actual YF-22 and YF-23 prototypes when they were in flight?
Both designs had the correct shaping to their outer machine lines in order to minimize radar cross-section, but there is a noticeable difference between those prototypes and, say, the production F-22 in terms of very small details i.e. RAM inlays, putties, tapes around doors, etc. A similar phenomenon was observed with the X-35 JSF when compared with the F-35 Lightning II development aircraft. That makes me wonder if such an RCS test was part of the ATF competition.