@Test
  public void testCountStringAllNull() throws HiveException {
    testAggregateString(
        "count",
        4,
        Arrays.asList(new Object[]{null, null, null, null, null}),
        0L);
  }
Unit test for the vectorized GROUP BY operator.
ql/src/test/org/apache/hadoop/hive/ql/exec/vector/TestVectorGroupByOperator.java