protected static Tool doMROnTableTest(HBaseTestingUtil util, String family, String data,
    String[] args, int valueMultiplier) throws Exception {
    TableName table = TableName.valueOf(args[args.length - 1]);
    Configuration conf = new Configuration(util.getConfiguration());

    // populate input file
    FileSystem fs = FileSystem.get(conf);
    Path inputPath =
      fs.makeQualified(new Path(util.getDataTestDirOnTestFS(table.getNameAsString()), "input.dat"));
    FSDataOutputStream op = fs.create(inputPath, true);
    op.write(Bytes.toBytes(data));
    op.close();
    LOG.debug(String.format("Wrote test data to file: %s", inputPath));

    if (conf.getBoolean(FORCE_COMBINER_CONF, true)) {
      LOG.debug("Forcing combiner.");
      conf.setInt("mapreduce.map.combine.minspills", 1);
    }

    // run the import
    List<String> argv = new ArrayList<>(Arrays.asList(args));
    argv.add(inputPath.toString());
    Tool tool = new ImportTsv();
    LOG.debug("Running ImportTsv with arguments: " + argv);
    try {
      // Job will fail if observer rejects entries without TTL
      assertEquals(0, ToolRunner.run(conf, tool, argv.toArray(args)));
    } finally {
      // Clean up
      if (conf.getBoolean(DELETE_AFTER_LOAD_CONF, true)) {
        LOG.debug("Deleting test subdirectory");
        util.cleanupDataTestDirOnTestFS(table.getNameAsString());
      }
    }

    return tool;
  }
Force use of combiner in doMROnTableTest. Boolean. Default is true.
hbase-mapreduce/src/test/java/org/apache/hadoop/hbase/mapreduce/TestImportTSVWithTTLs.java