public Result next(long scannerId) throws IOException {
    RegionNameAndIndex rnai = this.scannersAndOffsets.get(scannerId);
    int index = rnai.getThenIncrement();
    Result[] results = this.nexts.get(rnai.getRegionName());
    if (results == null) return null;
    return index < results.length ? results[index] : null;
  }
Use this method to set what a scanner will reply as we next through
hbase-server/src/test/java/org/apache/hadoop/hbase/master/MockRegionServer.java