It is surprising to me that most QRHs do not require a fire warning system test after completion of any fire drill.
Many years ago I experienced a momentary fire warning just after takeoff on a performance test flight in a brand new F27 that had only a few hours of ferry time. We were conducting 'hot and high' tests in temperatures approaching ISA plus 35.
The warning illuminated, but within a few seconds cancelled. Wrongly we assumed a false transient, caused we thought by the extremely hot ambient conditions. This was not uncommon in earlier versions of this aircraft type with the usual cure being to increase climb speed. Fortunately a deadheading pilot sitting in the passenger cabin saw the flames and yelled out to us.
After completing the drill and making an immediate landing we found that a combustion chamber had a faulty weld. This had opened up enough to allow hot flame to reach the fire wire and set off the warning. Then it opened more and became a blow torch which destroyed the complete loop system. The design was such that at that point the entire warning system was disabled. In the short time it had been burning through the combustion chamber, considerable damage had also been done to the engine control linkage for HP fuel.
So since then I have taught crews to conduct a fire test after any drill involving fire. If the system does not test, assume the worst and land RFN (right.......now)