JUnit tests fail during full build with a class not found error. Debugging the problem shows a dependency conflict with the security-core-api pulling in an older log4j-api. The new instances of the MiniSolrClouldCluster being created during the unit test utilize logging classes/methods only available in later versions of log4j.
Full build on OSX with Maven 3.5.4 and Java 1.8.0_181. Also replicated on Windows with Maven and Java just a few minor versions back.