@Test
  public void oplogWriteBufferSizeIsEqualsToDiskStoreWriteBufferSize() throws Exception {
    File[] diskDirs = new File[1];
    int expectedWriteBufferSize = 12345;
    diskDirs[0] = temporaryDirectory.newFolder("dir1");
    cache = createCache();
    cache.createDiskStoreFactory().setWriteBufferSize(expectedWriteBufferSize).setDiskDirs(diskDirs)
        .create(DISK_STORE_NAME);
    Region region = cache.<String, String>createRegionFactory(RegionShortcut.PARTITION_PERSISTENT)
        .setDiskStoreName(DISK_STORE_NAME).create(REGION_NAME);
    putEntries(region, 1);
    DiskStore diskStore = cache.findDiskStore(DISK_STORE_NAME);
    assertThat(diskStore.getWriteBufferSize()).isEqualTo(expectedWriteBufferSize);
    Oplog oplog = ((DiskStoreImpl) diskStore).getPersistentOplogs().getChild();
    assertThat(oplog.getWriteBuf().capacity()).isEqualTo(expectedWriteBufferSize);
  }
8 oplog files should be created.
The eighth one does not fit in dir1, so that directory should
be skipped, and the file should be stored in dir2.
geode-core/src/integrationTest/java/org/apache/geode/internal/cache/DiskStoreImplIntegrationTest.java