private Set<String> getBlobsInServers(MockServerLayout mockServerLayout) {
    Set<String> blobsInServers = new HashSet<>();
    for (MockServer mockServer : mockServerLayout.getMockServers()) {
      blobsInServers.addAll(mockServer.getBlobs().keySet());
    }
    return blobsInServers;
  }
Return the blob ids of all the blobs in the servers in the cluster.
@param mockServerLayout the {@link MockServerLayout} representing the cluster.
@return a Set of blob id strings of the blobs in the servers in the cluster.
ambry-router/src/test/java/com/github/ambry/router/NonBlockingRouterTest.java