Why doesn't this FOR set work?

To me, it seems that he required a new way of executing test processings in parallel on a machine with Multiple-core-CPU (e.g. AWS EC2 M5: 96 vCPU). I have invented it for Katalon Studio. See the following topic:

… sorry, I’m joking. I haven’t tested any project empowered by TestClosure on EC2 M5. Just I hoped it.