This question just occured to me while I was setting up my first manned (err, kerbalized?) Duna mission in KSP: In order to test my basic lander design I did not want to start a whole Duna Mission but thought of using it on Minmus first. So the ascent engines are used for landing/starting from a closer body with lower gravity.
However, what would NASA do with a manned Mars mission? Where there ever (or are there) plans to test a Mars lander on the moon first? Would that even work (is landing on and starting from the Moon possible with the delta-v required for landing on and starting from Mars)? How about the atmospheric reentry? Is there a way to test a Mars lander in Earth' atmosphere or would it simply not work here (heat shield, parachute design)? So how would NASA ensure that after a year long mission the lander/ascent stage actually works as expected?