@Override
      public String explainFailure() {
        return "expected largest region to be >= 4mb.";
      }
create a table with 5 regions, having region sizes so as to provoke a split of the largest
region.
<ul>
<li>total table size: 12</li>
<li>average region size: 2.4</li>
<li>split threshold: 2.4 * 2 = 4.8</li>
</ul>
hbase-server/src/test/java/org/apache/hadoop/hbase/master/normalizer/TestSimpleRegionNormalizerOnCluster.java