Albert: not really - programming port serial doesn't have a direct multi-byte read, it is too slow to need one. And an 888888888 byte test would take over 21 hours to run 
If you need a programming port loopback sketch use MultiSerialMega and connect pins 18 and 19. As for the 16u2 firmware it is almost the same as the Uno firmware and I have tested that to death 2 years ago - it can be tested by uploading Blink and linking pins 0 and 1.