During maintenance sometimes you will disconnect the weight on wheels switches and fool them into thinking the aircraft is airborne. Then you can do a "dummy retraction" with the gear pins in place and make sure all the hydraulics are working properly. The key is leaving the gear pins in! have seen this done many times, and only seen one dropped airplane. Most of the older generation of aircraft will allow you to raise the gear handle with the aircraft on the ground, the system is just locked out by the squat switches. Hope that is clear? Thought I would put my 2 cents in.