@Test
  public void testHelperAPIsForOverflowOnlyRegion() {
    diskProps.setPersistBackup(false);
    diskProps.setRolling(false);
    diskProps.setMaxOplogSize(1024 * 1024);
    diskProps.setSynchronous(true);
    diskProps.setOverflow(true);
    diskProps.setBytesThreshold(10000);
    diskProps.setTimeInterval(0);
    diskProps.setOverFlowCapacity(2);
    region = DiskRegionHelperFactory.getSyncOverFlowOnlyRegion(cache, diskProps);
    final byte[] val = new byte[1000];
    DiskRegion dr = ((LocalRegion) region).getDiskRegion();
    region.put("1", val);
    region.put("2", val);
    region.put("3", val);
    DiskEntry entry1 = (DiskEntry) ((LocalRegion) region).basicGetEntry("1");
    DiskEntry entry2 = (DiskEntry) ((LocalRegion) region).basicGetEntry("2");
    DiskEntry entry3 = (DiskEntry) ((LocalRegion) region).basicGetEntry("3");
    assertNull(entry2.getDiskId());
    assertNull(entry3.getDiskId());
    assertNotNull(entry1.getDiskId());
    assertNull(DiskEntry.Helper.getValueOnDisk(entry3, dr));
    assertNull(DiskEntry.Helper.getValueOnDisk(entry2, dr));
    assertNotNull(DiskEntry.Helper.getValueOnDisk(entry1, dr));
    assertNull(DiskEntry.Helper.getValueOnDisk(entry3, dr));
    assertNull(DiskEntry.Helper.getValueOnDisk(entry2, dr));

    assertNull(entry2.getDiskId());
    assertNull(entry3.getDiskId());
    assertNotNull(entry1.getDiskId());
    assertNull(DiskEntry.Helper.getValueOnDiskOrBuffer(entry3, dr, (LocalRegion) region));
    assertNull(DiskEntry.Helper.getValueOnDiskOrBuffer(entry2, dr, (LocalRegion) region));
    assertNotNull(DiskEntry.Helper.getValueOnDiskOrBuffer(entry1, dr, (LocalRegion) region));
    assertNull(DiskEntry.Helper.getValueOnDisk(entry3, dr));
    assertNull(DiskEntry.Helper.getValueOnDisk(entry2, dr));
  }
Tests the various DiskEntry.Helper APIs for correctness as there is now delayed creation of
DiskId and accessing OplogkeyId will throw UnsupportedException
geode-core/src/integrationTest/java/org/apache/geode/internal/cache/OplogJUnitTest.java