private void waitNumRolledLogFiles(AbstractFSWAL<?> wal, int expected) {
    TEST_UTIL.waitFor(5000, () -> wal.getNumRolledLogFiles() == expected);
  }
tests the log comparator. Ensure that we are not mixing meta logs with non-meta logs (throws
exception if we do). Comparison is based on the timestamp present in the wal name.
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/wal/AbstractTestFSWAL.java