A jumper wire across the rain sensor terminals indeed simulates a closed sensor. However, the type ‘normally closed’, or ‘normally open’ is a software thing defined in the options. For example, if you choose the rain sensor type as ‘normally closed’, then the controller assumes:
– there is no rain when the two pins are shorted (i.e. jumper wire is inserted)
– rain is detected when the two pins are open (i.e. jumper wire is removed)
If you choose the rain sensor type as ‘normally open’, then the logic is reversed.