While some utility libraries build on some JUnit 4 functionality, it may still be possible to use them either via JUnit 4 rules, which TestBalloon supports, or in a decoupled, Kotlin-first way, in which case an integration should always be possible without too much effort. A remarkable example is
the Robolectric case, which seemed impossible at first, but then turned out to be surprisingly simple to integrate. I haven't really looked into Paparazzi in this regard, so mileage may vary of course.