CachedDcDomainTestCase has the same problem that led to the odd lifecycle handling in ReadOnlyModeTestCase that will be corrected in
It uses DomainTestSupport.stop() as a shorthand for stopping the HCs, rather than using the DomainLifecycleUtil for those HCs to stop them. The problem is DomainTestSupport.stop() also closes down the Endpoint that is used by those DomainLifecycleUtil instances. The instances remain though and are still used. The problem is once the Endpoint is stopped, those DomainLifecycleUtil instances can no longer connect to the HCs. So all the util code in DomainLifecycleUtil for executing ops or managing HC lifecycle no longer works.
The result is CachedDcDomainTestCase has all sorts of custom lifecycle code that's a possible source of bugs.