Tagging a test as 'medium' means that the test class has the following characteristics:
it can be executed in an isolated JVM (Tests can however be executed in different JVMs on
the same machine simultaneously so be careful two concurrent tests end up fighting over ports
or other singular resources).
ideally, the whole medium test-suite/class, no matter how many or how few test methods it
has, will complete in 50 seconds; otherwise make it a 'large' test.
Use it for tests that cannot be tagged as 'small'. Use it when you need to start up a cluster.