@Override
      public FSDataInputStream answer(InvocationOnMock invocation) throws Throwable {
        Thread.sleep(1500); // Sleep a while and wait report status invoked
        return (FSDataInputStream) invocation.callRealMethod();
      }
@param spiedFs should be instrumented for failure.
hbase-server/src/test/java/org/apache/hadoop/hbase/wal/TestWALSplit.java