private static ClientProtocol getNamenode(DFSClient dfsc) throws Exception {
    Field nf = DFSClient.class.getDeclaredField("namenode");
    nf.setAccessible(true);
    return (ClientProtocol) nf.get(dfsc);
  }
Test that the hook works within HBase, including when there are multiple blocks.
hbase-server/src/test/java/org/apache/hadoop/hbase/fs/TestBlockReorderMultiBlocks.java