@Override
      protected void bulkLoadPhase(AsyncClusterConnection conn, TableName tableName,
        Deque<LoadQueueItem> queue, Multimap<ByteBuffer, LoadQueueItem> regionGroups,
        boolean copyFiles, Map<LoadQueueItem, ByteBuffer> item2RegionMap) throws IOException {
        int i = attemptedCalls.incrementAndGet();
        if (i == 1) {
          // On first attempt force a split.
          forceSplit(table);
        }
        super.bulkLoadPhase(conn, tableName, queue, regionGroups, copyFiles, item2RegionMap);
      }
This test exercises the path where there is a split after initial validation but before the
atomic bulk load call. We cannot use presplitting to test this path, so we actually inject a
split just before the atomic region load.
hbase-server/src/test/java/org/apache/hadoop/hbase/tool/TestBulkLoadHFilesSplitRecovery.java