LEO Progress: J-2X to Test Stand A1, NASA Blog (Liquid Rocket Engines)
"Recently, J-2X development engine 10002 was on the road. If you remember, E10002 went through a six-test series on test stand A2 that began in February and finished up in April. The next planned phase of E10002 testing is on test stand A1. In between these series, the engine was back in the assembly area of NASA Stennis Space Center Building 9101.
This respite between test series allowed for a complete series of inspections of the engine hardware. This is vital piece of the learning process for engine development. The basic truth is that a rocket engine is just darn tough on itself when it fires. The reason that we test and test and test is to make sure that our design can stand up to the recurring brutal conditions. The chance to look for the effects of that testing through detailed inspections away from the test stand is an opportunity to collect a great deal of useful information. "