private void loadData(Table table) throws IOException {
    for (int i = 0; i < ROWSIZE; i++) {
      Put put = new Put(ROWS[i]);
      put.addColumn(FAMILYNAME, QUALIFIER, Bytes.toBytes(i));
      table.put(put);
    }
  }
This test tests 1, merging region not online; 2, merging same two regions; 3, merging unknown
regions. They are in one test case so that we don't have to create many tables, and these tests
are simple.
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestRegionMergeTransactionOnCluster.java