@Override
        public void preLogRoll(Path oldFile, Path newFile) {
          LOG.debug("preLogRoll: oldFile=" + oldFile + " newFile=" + newFile);
          preLogRolledCalled.add(1);
        }
Test that WAL is rolled when all data nodes in the pipeline have been restarted.
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/wal/TestLogRolling.java