@Override
    public List<String> getStoppedReplicas() {
      return stoppedReplicas.stream().map(r -> r.getPartitionId().toPathString()).collect(Collectors.toList());
    }
Ctor for MockClusterParticipant with arguments to override return value of some methods.
@param setSealStateReturnVal if not null, use this value to override result of setReplicaSealedState(). If null,
                             go through standard workflow in the method.
@param setStopStateReturnVal if not null, use this value to override result of setReplicaStoppedState(). If null,
                             go through standard workflow in the method.
ambry-store/src/test/java/com/github/ambry/store/StorageManagerTest.java