The infamous N757A “Catfish” was the first Boeing 757-200 ever built. It was later extensively modified for use by Lockheed Martin as a testbed for F-22 and F-35 sensor and avionics integration.
Boeing fitted this aircraft with a canard above its cockpit so as to simulate F-22 and F35 wing sensor layout. The mid section had a 32 seat laboratory with Electronic Warfare (EW), computers, communication, identification and navigation sensors including an F-22 cockpit.
The present status of the aircraft is unknown. However it is also reported that in similar manner China’s stealth fighter J-20 avionics systems where tested on a highly modified Russian Tupolev Tu-204C twinjet airliner.
India may have to get access to such a platform in near future to validate the ambitious 5th generation fighter aircraft AMCA avionics. Therefore, India may also have to choose between Russia and America for validating AMCA.
India will in sometime need its own flying test bed, either an Airbus A340 or an Il78 to test engines. We already have an Airbus A319 to test our electronic systems. With Tejas MK2, TEDBF, AMCA, etc in pipeline it has become a necessity.