void addStore(PartitionId partitionId, ReplicationTest.StoreEventListener listener) {
    storesByPartition.computeIfAbsent(partitionId, partitionId1 -> new InMemoryStore(partitionId,
        infosByPartition.computeIfAbsent(partitionId1,
            (Function<PartitionId, List<MessageInfo>>) partitionId2 -> new ArrayList<>()),
        buffersByPartition.computeIfAbsent(partitionId1,
            (Function<PartitionId, List<ByteBuffer>>) partitionId22 -> new ArrayList<>()), listener));
  }
Adds an in-memory store to a partition if not present already
@param partitionId partition id
@param listener listener for store events
ambry-replication/src/test/java/com/github/ambry/replication/MockHost.java