Add a log when SIGKILL is sent to a test parallel worker

Author: mame

tool/lib/test/unit.rb

@@ -416,6 +416,7 @@ def quit(reason = :normal)
 
         def kill
           Process.kill(:KILL, @pid)
+          warn "worker #{@pid} does not respond; SIGKILL is sent"
         rescue Errno::ESRCH
         end