I guess silent running test while pirate on tail isn't the best idea. On my early days I attempted to do iSlave smuggle run. Found low cost supply and high paying demand, 8 jumps away. Did read how smuggling work, prepared ship, bound silent running, had everything set. In theory. Bought cargo and started to fly. Immediately got pirate tail, no big deal, avoiding them is easy. I was jumping from system to system so fast that pirate couldn't manage to keep up so I forgot about him as I was focused on proper SC drop and silent station approach. 1 jump before destination I decided to perform dry test - dropped from SC, hit silent running (shields dropped to my surprise), watched how fast temp rose (not that bad). At 120% I turned SR off and prepared to make final jump. Test completed, all set.
And then pirate dropped into my instance... still had over 100% heat, no shields and weak hull. Two or three shots after I was admiring rebuy screen.