No, running the spindle with or without any tool inserted and without machining any material.

And yes now I remember that when I connected the water hose some days ago I forgot to reconnect the motor power plug and started it for a few seconds without the motor.

After that it has run ok for about half an hour until I have applied some load (4mm end mill 3mm deep in acrylic), the bit didn't broke and the cut was clean.