private FakeCaptureVectorToRowOutputOperator.OutputInspector init(
          String aggregateName, Map<Object,Object> expected, Set<Object> keys) {
        this.aggregateName = aggregateName;
        this.expected = expected;
        this.keys = keys;
        return this;
      }
Unit test for the vectorized GROUP BY operator.
ql/src/test/org/apache/hadoop/hive/ql/exec/vector/TestVectorGroupByOperator.java