[avar]

They've already had Dragon flights where they've said "if there were humans aboard, they'd have been just fine", i.e. the Dragon's life-support capabilities have been tested.

You don't have to have flown humans to test whether you can fly humans, you know you were able to maintain a breathable atmosphere, and you know you have enough fuel to launch a few hundred kilos of meatbags, food & water.

[greglindahl]

Note also that SpaceX is going to start flying cargo in a derived-from-Crew-Dragon Dragon, so they'll have more experience with the changes in Crew Dragon, and can practice propulsive landings on Earth for cargo before trying it for crew.