public void testSum() {
    assertThat(emptyAccumulator.sum()).isWithin(0.0).of(0.0);
    assertThat(emptyAccumulatorByAddAllEmptyIterable.sum()).isWithin(0.0).of(0.0);
    assertThat(emptyAccumulatorByAddAllEmptyStats.sum()).isWithin(0.0).of(0.0);
    assertThat(oneValueAccumulator.sum()).isWithin(ALLOWED_ERROR).of(ONE_VALUE);
    assertThat(oneValueAccumulatorByAddAllEmptyStats.sum()).isWithin(ALLOWED_ERROR).of(ONE_VALUE);

  }

  public void testSum() {
    assertThat(EMPTY_STATS_VARARGS.sum()).isEqualTo(0.0);
    assertThat(EMPTY_STATS_ITERABLE.sum()).isEqualTo(0.0);
    assertThat(ONE_VALUE_STATS.sum()).isWithin(ALLOWED_ERROR).of(ONE_VALUE);
    assertThat(TWO_VALUES_STATS.sum()).isWithin(ALLOWED_ERROR).of(TWO_VALUES_MEAN * 2);
    assertThat(MANY_VALUES_STATS_VARARGS.sum())
        .isWithin(ALLOWED_ERROR)

  public void testSum() {
    assertThat(emptyAccumulator.sum()).isWithin(0.0).of(0.0);
    assertThat(emptyAccumulatorByAddAllEmptyIterable.sum()).isWithin(0.0).of(0.0);
    assertThat(emptyAccumulatorByAddAllEmptyStats.sum()).isWithin(0.0).of(0.0);
    assertThat(oneValueAccumulator.sum()).isWithin(ALLOWED_ERROR).of(ONE_VALUE);
    assertThat(oneValueAccumulatorByAddAllEmptyStats.sum()).isWithin(ALLOWED_ERROR).of(ONE_VALUE);

  }

  public void testSum() {
    assertThat(EMPTY_STATS_VARARGS.sum()).isEqualTo(0.0);
    assertThat(EMPTY_STATS_ITERABLE.sum()).isEqualTo(0.0);
    assertThat(ONE_VALUE_STATS.sum()).isWithin(ALLOWED_ERROR).of(ONE_VALUE);
    assertThat(TWO_VALUES_STATS.sum()).isWithin(ALLOWED_ERROR).of(TWO_VALUES_MEAN * 2);
    assertThat(MANY_VALUES_STATS_VARARGS.sum())
        .isWithin(ALLOWED_ERROR)

    assertThat(TWO_VALUES_PAIRED_STATS.sampleCovariance())
        .isWithin(ALLOWED_ERROR)
        .of(TWO_VALUES_SUM_OF_PRODUCTS_OF_DELTAS);
    assertThat(MANY_VALUES_PAIRED_STATS.sampleCovariance())
        .isWithin(ALLOWED_ERROR)
        .of(MANY_VALUES_SUM_OF_PRODUCTS_OF_DELTAS / (MANY_VALUES_COUNT - 1));
    assertThat(HORIZONTAL_VALUES_PAIRED_STATS.sampleCovariance()).isWithin(ALLOWED_ERROR).of(0.0);

    assertThat(TWO_VALUES_PAIRED_STATS.sampleCovariance())
        .isWithin(ALLOWED_ERROR)
        .of(TWO_VALUES_SUM_OF_PRODUCTS_OF_DELTAS);
    assertThat(MANY_VALUES_PAIRED_STATS.sampleCovariance())
        .isWithin(ALLOWED_ERROR)
        .of(MANY_VALUES_SUM_OF_PRODUCTS_OF_DELTAS / (MANY_VALUES_COUNT - 1));
    assertThat(HORIZONTAL_VALUES_PAIRED_STATS.sampleCovariance()).isWithin(ALLOWED_ERROR).of(0.0);

    int expectedHashCode = 0;
    for (E element : getSampleElements()) {
      expectedHashCode += ((element == null) ? 0 : element.hashCode());
    }
    assertEquals(
        "A Set's hashCode() should be the sum of those of its elements.",
        expectedHashCode,
        getSet().hashCode());
  }

  @CollectionSize.Require(absent = CollectionSize.ZERO)
  @CollectionFeature.Require(ALLOWS_NULL_VALUES)

    add(-1L);
  }

  /**
   * Returns the current sum. The returned value is NOT an atomic snapshot; invocation in
   * the absence of concurrent updates returns an accurate result, but concurrent updates that occur
   * while the sum is being calculated might not be incorporated.
   *
   * @return the sum
   */
  @Override
  public long sum() {
    long sum = base;
    Cell[] as = cells;
    if (as != null) {

    }
  }

  /** getAndAccumulate with sum adds given value to current, and returns previous value */
  public void testGetAndAccumulateWithSum() {
    AtomicDoubleArray aa = new AtomicDoubleArray(SIZE);
    for (int i : new int[] {0, SIZE - 1}) {
      for (double x : VALUES) {
        for (double y : VALUES) {
          aa.set(i, x);
          double z = aa.getAndAccumulate(i, y, Double::sum);
          assertBitEquals(x, z);

                }
              }));
    }
    threadPool.shutdown();
    assertTrue(threadPool.awaitTermination(300, SECONDS));
    long sum = 0;
    for (Future<Long> f : futures) {
      sum += f.get();
    }
    assertEquals(sum, map.get(key));
  }