It looks like an uncaught exception not on the main thread allows the tests to continue and pass:
https://circleci.com/gh/mediachain/mediachain/48
(scroll down to java.lang.StackOverflowError in the sbt test step)
Is there a way to make the CI fail this? As far as I can tell, SBT doesn’t handle the exception correctly but maybe there’s another way to catch thread death?