Here's the current state of running our test suite of Java 9: https://gist.github.com/retronym/65527edfa7dcb4a4e905f364db9788d3 That's based on sbt testAll on the tip of scala/scala#6733. I expect the majority of failures will just requires some changes to the test themselves. Getting these working will let us include Java 9/10 in our CI.