@Test
  public void testMapRedPlan4() throws Exception {

    LOG.info("Beginning testMapPlan4");
    populateMapRedPlan4(db.getTable(Warehouse.DEFAULT_DATABASE_NAME,
        "src"));
    executePlan();
    fileDiff("kv1.string-sorted.txt", "mapredplan4.out");
  }
test reduce with multiple tagged inputs.
ql/src/test/org/apache/hadoop/hive/ql/exec/TestExecDriver.java