Currently we have the old replication tests indirectly testing PSYNC, however the most interesting part of the PSYNC code, that is, partial resynchronization, is currently not tested.

New tests should be added simulating connection issues and checking if after psync DEBUG POPULATE matches between instances.

During development this code paths were tested both in synthetic tests and setting up over WAN replication setups for weeks waiting for disconnections, however we definitely need unit tests for all the PSYNC main code paths.

This must be done before the 2.8 release.