@Override
    public void preGetOp(final ObserverContext<? extends RegionCoprocessorEnvironment> e,
      final Get get, final List<Cell> results) throws IOException {
      Threads.sleep(SLEEP_TIME);
    }
This copro sleeps 20 second. The first call it fails. The second time, it works.
hbase-server/src/test/java/org/apache/hadoop/hbase/client/AbstractTestCITimeout.java