The current CircleCI config could use some cleanup and improvements. First of all, the config has been made more modular by using the new CircleCI 2.1 executors and command elements. Based on
CASSANDRA-14713, there's now also a Java 11 executor that will allow running tests under Java 11. The build step will be done using Java 11 in all cases, so we can catch any regressions for that and also test the Java 11 multi-jar artifact during dtests, that we'd also create during the release process.
The job workflow has now also been changed to make use of the manual job approval feature, which now allows running dtest jobs only on request and not automatically with every commit. The Java8 unit tests still do, but that could also be easily changed if needed. See example workflow with start_ jobs being triggers needed manual approval for starting the actual jobs.