[londons_explore]

I assume it was tested in a pressure chamber on earth to simulate the pressure and composition of Mars atmosphere.

Obviously it wouldn't be able to fly in the pressure chamber due to increased gravity, but by suspending it on elastic you can still test that the blade functions as intended.

The only bit you can't really fully test is the constants for the control loops in the flight control algorithm, but I assume they chose them with a lot of stability margin.

[SideburnsOfDoom]

> I assume it was tested in a pressure chamber on earth... by suspending it on elastic you can still test that the blade functions as intended

They did exactly that. NASA has a big (adjustable) vacuum chamber for this kind of purpose.

This comment links to video: https://news.ycombinator.com/item?id=28432811

[_Microft]

It did fly in the vacuum chamber. It was a tethered flight and the difference between Earth‘s and Mars‘s gravity was compensated by an appropriate pull being applied to the tether.