> They might not have, because it might just fall out of the sky. It's built to overcome Mars' gravity, not Earth's.
A video has them flying that thing inside a pressure chamber without payload, so at least in this configuration it has enough power to overcome Earth's gravity. Probably wouldn't lift off on Earth with the payload, though.
However I agree with you, they will be testing it extensively in as close to Martian conditions as they can achieve.