@Override
      public String explainFailure() throws Exception {
        return "Eviction never happened.";
      }
Tests the concurrent LruAdaptiveBlockCache.
<p>
Tests will ensure it grows and shrinks in size properly, evictions run when they're supposed to
and do what they should, and that cached blocks are accessible when expected to be.
hbase-server/src/test/java/org/apache/hadoop/hbase/io/hfile/TestLruAdaptiveBlockCache.java