I'm sure this has been repeatedly asked/answered, but how do you actually run tests in the mpp?

I think you have to run the tests for the individual platforms. I found it easier to iterate by just running jvm tests first and then verify on all periodically.

I'm explicitly trying to run some native stuff to play around with the runtime, so I need native. Clion plugin appears to be not functional today for some reason

Native is not supported by IDEA CE as of today. I had to run tests with gradle. For js, I think that nothing is supported on IDEA CE. It just generates the js file and the js test file. I wrote a simple HTML web page that runs the test in browser with mocha and a gradle task to launch it. You can have a look at it here : https://github.com/tokou/coinche

I just get a Run Configuration from the Gradle window and run tests on native from there

I generally run from command line. Updated config to look more like coinche. See how it goes.

There’s also ios-specific config for running device/simulator tests in the kotlin-mpp-example, if you haven’t seen that yet https://github.com/JetBrains/kotlin-mpp-example/blob/master/greeting/build.gradle#L80-L92