I also have a doubt about the browser’s capability to run in parallel on a single machine.
When I run multiple Test Suites each of which opens a Chrome browser, I can see in the Task Manager that multiple processes of Chrome are launched.
Do these Chrome processes are acting in parallel?
No. As far as I observed, Chrome processes never make multiple HTTP Request-Response conversations in parallel. I observed Chrome process#1 and Chrome process#2 acted just sequentially. While the process#1 is in action (send request and wait for the response), then the process#2 waits blocked for the prior conversation to finish.
I think, this is how Chrome is designed. Remember, a browser is an agent for human user who slowly operates UI interactively with his/her fingers. I guess that Chrome is well-engineered that it controls the consumption of the given hardware resources (especially IO to network) moderate not to exceed the limit.
Yes, we can tell Katalon’s Test Suites processes to run in parallel. But in the background, I believe, the Chrome processes work effectively sequentially. Katalon is unable to change the way how Chrome behaves. So, I think, the parallel mode of Katalon’s Test Suite Collection is a fake. It makes you to misunderstand that you can make everything to perform in parallel, but in fact the system does not work as such.
Rule of thumb; if you want 3 Chrome processes to act really in parallel, you need 3 machines.