@Override
      public boolean evaluate() throws Exception {
        return cache.getStats().getEvictionCount() > 0;
      }
Tests the concurrent LruBlockCache.
<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/TestLruBlockCache.java