@Test
  public void testChannelWriteRetriesOnFailureDuringFlush() throws Exception {
    DiskRegionProperties props = new DiskRegionProperties();
    props.setOverFlowCapacity(1);
    region = DiskRegionHelperFactory.getSyncOverFlowOnlyRegion(cache, props);
    region.put("K1", "v1"); // add two entries to make it overflow
    region.put("K2", "v2");
    DiskRegion dr = ((LocalRegion) region).getDiskRegion();
    OverflowOplog oplog = dr.getDiskStore().overflowOplogs.getActiveOverflowOplog();
    assertNotNull("Unexpected null Oplog for " + dr.getName(), oplog);
    doChannelFlushWithFailures(oplog, 1 /* write failure */);
  }
This method tries to write half of the byte buffer to the channel.
geode-core/src/integrationTest/java/org/apache/geode/internal/cache/OverflowOplogFlushTest.java