"Nobody knows? Test with water discharge?" Really? You cannot be serious.

Underwriters Laboratory & NFPA have all worked to test & design reliable, long life working sprinkler heads for decades. Testing has proven they will work when needed.  http://www.sfpe.org/page/2012_Q2_3

Simple in design, heat sensitive glass vial will break when heated to design temp, water comes out.  https://www.tyco-fire.com/index.php?P=detailprod&S=3190

Next time do your due diligence before posting.