boolean isOplogToBeCompactedAvailable(DiskStoreImpl ds) {
    if (ds.getOplogToBeCompacted() == null) {
      return false;
    }
    return ds.getOplogToBeCompacted().length > 0;
  }
Verifies that the region is recovered from Oplog's (including .drf only oplog's) when cache is
closed and then recreated again in order to trigger recovery.
This test case covers the following scenario:

1. Create several Oplog files (.crf, .drf and .krf) by executing put operations
2. Execute destroy operation for every fifth entry, and each time add new entry. This will
result with few additional Oplog files. Compaction threshold will not be reached.
3. Destroy all operations created in step 2. This will trigger compaction of files that
were created in step 2. Compaction will delete only .crf and .krf files, but will not
delete .drf files because they contain destroy operations for events located in
.crf files created in step 1.
4. At this step there will be Oplog objects from step 1. that will contain all files (.crf,
.drf and .krf), and Oplog objects from step 2. that will contain only .drf files.
In order to test recovery, close the cache and then recreate it again.
5. Check that region is recovered correctly. Check that only events that have never been
destroyed are recovered from Oplog files.
6. Check that unnecessary objects are cleared for theOplog that represents orphaned .drf
file (no accompanying .crf and .krf file)
geode-core/src/integrationTest/java/org/apache/geode/internal/cache/DiskRegionCompactorClearsObjectThatAreNoLongerNeededIntegrationTest.java