The new firmware from Castle allows to check the motor Kv. And it's a no load test according to the manual, for example result is 2500Kv for the 1515/1Y 2200Kv motor (2200Kv is the Kv measured at load or max efficiency).
So I would say without load.
Inferno VE MMv3 NEU-CC 1515/1Y 4S "Flying machine"