Test your lander prototype's thrust sysyem, GNC Sensors, RCS methods on Moon Gravity Simulator System.
Try your lander prototype's landing gear, footpad, shock absorber, structure etc. on Lunar soil simulant.
You can test the sensors, electronic components, and avionics systems you plan to use in your lunar lander under operation conditions.
You can test your lunar lander's Guidance Navigation & Control Systems under Moon-like conditions.