There isn't any general mocking framework like Mockk that works on native, though there's a few that will work for interfaces but not classes. I generally recommend against testing only on JVM, because you'll miss issues that are native-specific. But it can be a good first step if you're moving code into common and want to make sure you don't break existing JVM usage.
Also, this isn't really a Touchlab-specific question, so you'd probably get more advice if you ask in #multiplatform instead.