@Override
    protected RegionScannerImpl instantiateRegionScanner(Scan scan,
      List<KeyValueScanner> additionalScanners, long nonceGroup, long nonce) throws IOException {
      if (scan.isReversed()) {
        if (scan.getFilter() != null) {
          scan.getFilter().setReversed(true);
        }
        return new HeartbeatReversedRegionScanner(scan, additionalScanners, this);
      }
      return new HeartbeatRegionScanner(scan, additionalScanners, this);
    }
Custom HRegion class that instantiates {@link RegionScanner}s with configurable sleep times
between fetches of row Results and/or column family cells. Useful for emulating an instance
where the server is taking a long time to process a client's scan request
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestScannerHeartbeatMessages.java