@Override
    public InternalScanner preCompact(ObserverContext<? extends RegionCoprocessorEnvironment> c,
      Store store, InternalScanner scanner, ScanType scanType, CompactionLifeCycleTracker tracker,
      CompactionRequest request) throws IOException {
      return new ShippedObservingScanner(scanner);
    }
Verifies that if a coproc returns an InternalScanner which implements Shipper, the shippped
method is appropriately called in Compactor.
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestCompactionWithShippingCoprocessor.java