If you really need to test it you can run the airspeed up carefully with a large syringe and appropriate tubing. Be careful you don;t pump in too much pressure.

A safer method is to just go to the menu under Hardware and Digital Inputs and check that the boxes for input 1 and 2 are green when the selected statements are true and red when they aren't. This checks your switches and as long as the firmware hasn't been updated if the warnings worked before they should work again.