@Test
  public void testCombiner() throws IOException {
    Configuration conf = new Configuration(UTIL.getConfiguration());
    // force use of combiner for testing purposes
    conf.setInt("mapreduce.map.combine.minspills", 1);
    runTestOnTable(UTIL.getConnection().getTable(MULTI_REGION_TABLE_NAME));
  }
Test a map/reduce against a multi-region table
hbase-mapreduce/src/test/java/org/apache/hadoop/hbase/mapreduce/TestTableMapReduceBase.java