public long getEstimatedUniqueCount() {
        if (estimatedUniqueCount == UNDEFINED) {
            updateEstimate();
        }
        return estimatedUniqueCount;
    }
@Test
    public void requireThatEstimateIsCorrect() {
        ExpressionCountAggregationResult aggr = createAggregationWithSparseSketch(42);
        assertTrue(aggr.getEstimatedUniqueCount() == 1);
    }