PoolManagerImpl is an internal class in Geode, it may change or be removed at any time.
This installing a mock object into a Geode singleton. This may cause strange behavior in future tests that are running in the same JVM.
In this case, I think this use of PoolManagerImpl looks like it should be easy to remove. If ContiniousQueryListenerContainer provided a way to inject an object to be used to look up Pools, rather than directly depending on the static PoolManager.find method, the test could avoid having to change the real Geode singleton