@Override
  public void onBlobReplicaReplicated(String sourceHost, int port, String blobId, BlobReplicaSourceType sourceType) {
    objectTracker.computeIfAbsent(blobId, k -> new EventTracker(1)).trackReplicate(sourceHost, port);
  }
A mock notification system that helps to identify when blobs
get replicated. This class is not thread safe
ambry-test-utils/src/main/java/com/github/ambry/server/MockNotificationSystem.java