@BeforeClass
  public static void provisionCluster() throws Exception {
    conf = util.getConfiguration();
    // We don't check persistence in HFiles in this test, but if we ever do we will
    // need this where the default hfile version is not 3 (i.e. 0.98)
    conf.setInt("hfile.format.version", 3);
    conf.set("hbase.coprocessor.region.classes", TTLCheckingObserver.class.getName());
    util.startMiniCluster();
  }
Force use of combiner in doMROnTableTest. Boolean. Default is true.
hbase-mapreduce/src/test/java/org/apache/hadoop/hbase/mapreduce/TestImportTSVWithTTLs.java