My company has recently started to test the stable release through automation for which we are using the Katalon Studio as an automation tool.
How Katalon Studio works with the JUnit, TestNG?
At the moment (Release 5.0.1) it is not possible to import your JUnit/TestNG code to Katalon Studio. Means, you have to write new test scripts. But you can import third party libraries to your code, to do all the automation stuff like in your JUnit test cases.