Interesting craft in that it's essentially just a larger version of the R/C toys you can buy. I wonder how they tested the blade design. Did they fly it at 100,000ft on Earth?
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.
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.
I'm really interested to see how far consumer electronics will actually be proved useful in space. There's this perception that designing for space is ultra-difficult and requires n-tuple redundancy and specially fabricated radiation-hardened processors etc. but I wonder how much of that is just because when you're spending a billion dollars on a mission you REALLY don't want to lose it to some random bit flip and so you drop $100mil on goldplating the absolute heck out of everything.