@Override
      public Void call() throws Exception {
        LOG.info("Acquiring row lock");
        RowLock rl = region.getRowLock(b);
        obtainedRowLock.countDown();
        LOG.info("Waiting for 5 seconds before releasing lock");
        Threads.sleep(5000);
        LOG.info("Releasing row lock");
        rl.release();
        return null;
      }
Test RegionTooBusyException thrown when region is busy
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestHRegion.java