@Nonnull
  @Override
  public Sketch<IntegerSummary> getResult() {
    return unionAll();
  }
@Test
  public void testAccumulatorWithSingleSketch() {
    IntegerSketch input = new IntegerSketch(_lgK, IntegerSummary.Mode.Sum);
    IntStream.range(0, 1000).forEach(i -> input.update(i, 1));
    CompactSketch<IntegerSummary> sketch = input.compact();

    TupleIntSketchAccumulator accumulator = new TupleIntSketchAccumulator(_setOps, _nominalEntries, 2);
    accumulator.apply(sketch);

    Assert.assertFalse(accumulator.isEmpty());
    Assert.assertEquals(accumulator.getResult().getEstimate(), sketch.getEstimate());
  }