We’ve seen a previous video on the evolution of the J-2X rocket engine. As I posted before, the original J-2 was used on the second (S-II) and third (S-IVB) stages of the mighty Saturn V moon rocket. The J-2X update work was begun as part of the now-defunct Constellation project, and it is being continued under the new Space Launch System project that replaced Constellation.
Now NASA has begun a second round of testing on the J-2X on the revised A-2 Test Stand at NASA’s Stennis Space Center in Mississippi.
They also released a time lapse video of the J-2X being installed in the test stand: