There appears to be a bug here: https://github.com/kotest/kotest/blob/master/kotest-core/src/commonMain/kotlin/io/kotest/core/extensions/RuntimeTagExtension.kt#L34 . Shouldn't it be a var not a val?

Yep, you're right

Trying to PR but having trouble running the repo tests; getting "Could not resolve org.gradle.kotlin😛lugins:1.3.6." - do I have to configure any settings or should

./gradlew test

work out of the box?

It should work out of the box