Air carrier flight crew reported cargo compartment fire warning system malfunction.

Narrative

During the fire detection test we had a Smoke Warning Indication on EICAS and Fire Ext bottom illuminated on the overhead panel. We waited around 10 seconds to repeat the test with the same results. Before I started the APU I called Maintenance and they MEL the Fire Extinguishing System for the baggage compartment after two more tests having the same indications. During the boarding process; one of the Ground Crew reported to me that he smelled some smoke from the back of the aircraft. I went outside and smelled something weird around the tail of the aircraft with the APU running but no physical evidence of fire or smoke inside the Cargo Area; inside or outside the aircraft. I called company maintenance to reported and deplaned the aircraft and notified ZZZ Ground to send the fire trucks to inspect the aircraft. After inspection no evidence of fire or smoke was found. After one hour contract Maintenance arrived to the aircraft to inspect it with no evidence found. Flight continues to ZZZ1. No [priority handling was requested]. Aircraft was parked at gate. Probably some wire loops burned.