Yes, Chernobyl was a stupid disaster (though I would blame the delay of the test more than the test itself). Chernobyl was also unusually expensive since today's plants at least can't literally explode.

But human error happens and has to be in your risk calculation. Just like natural disasters happen (Fukushima was insured, just not against earthquakes, tsunamis and the like)

Edit: for context, "unusually expensive" means we hope to get the whole thing fixed within the 21st century.