The landing procedure of Curiosity on Mars has been described as a real challenge in part because of the powered descent stage and sky crane. Indeed the separation of Curiosity with the backshell + parachute occurred at an altitude of 1.8km at a velocity of 100m/s. The powered descent stage has then brought the sky crane with Curiosity to a stop at an altitude of a couple of meters and then hovered for about 15 seconds.
Has there been any tests on Earth of the powered descent stage's drop and hovering before sending it to Mars ? and powered descent stage + sky crane tests ? Are there any videos of these tests?