@Override
      public boolean advance() throws IOException {
        index++;
        return index < cells.size();
      }
Test filter. Filter will filter out any write time that is <= 5 (BOUNDARY). We count how many
items we filter out and we count how many cells make it through for distribution way down below
in the Table#batch implementation. Puts in place a custom DevNullConnection so we can insert
our counting Table.
hbase-server/src/test/java/org/apache/hadoop/hbase/replication/regionserver/TestWALEntrySinkFilter.java