What’s the recommended way to use kotlin.test or kotlintest in IntelliJ projects?

what do you mean?

How do you add kotlin.test library to an IntelliJ project to use assertion functions and annotations in tests? Same question about kotlintest.

are you using maven or gradle?

None. Just IntelliJ.

If you aren't using maven or gradle, you'll need to add the kotlin.test jar to the classpath yourself.