*/
  @Override
  public boolean equals(@Nullable Object obj) {
    if (obj == null) {
      return false;
    }
    if (getClass() != obj.getClass()) {
      return false;
    }
    PairedStats other = (PairedStats) obj;
    return xStats.equals(other.xStats)
        && yStats.equals(other.yStats)
        && doubleToLongBits(sumOfProductsOfDeltas) == doubleToLongBits(other.sumOfProductsOfDeltas);
  }

  /**

 * {@link PairedStatsAccumulator#add}, and various error cases of that method. For tests of the
 * {@link PairedStatsAccumulator#snapshot} method which returns {@link PairedStats} instances, see
 * {@link PairedStatsTest}.
 *
 * @author Pete Gillin
 */
@NullUnmarked
public class PairedStatsAccumulatorTest extends TestCase {

  private PairedStatsAccumulator emptyAccumulator;

        .addEqualityGroup(
            new PairedStats(MANY_VALUES_STATS_ITERABLE, OTHER_MANY_VALUES_STATS, 1.23),
            new PairedStats(MANY_VALUES_STATS_VARARGS, OTHER_MANY_VALUES_STATS, 1.23))
        .addEqualityGroup(
            new PairedStats(OTHER_MANY_VALUES_STATS, MANY_VALUES_STATS_ITERABLE, 1.23))
        .addEqualityGroup(
            new PairedStats(MANY_VALUES_STATS_ITERABLE, MANY_VALUES_STATS_ITERABLE, 1.23))

        .addEqualityGroup(
            new PairedStats(MANY_VALUES_STATS_ITERABLE, OTHER_MANY_VALUES_STATS, 1.23),
            new PairedStats(MANY_VALUES_STATS_VARARGS, OTHER_MANY_VALUES_STATS, 1.23))
        .addEqualityGroup(
            new PairedStats(OTHER_MANY_VALUES_STATS, MANY_VALUES_STATS_ITERABLE, 1.23))
        .addEqualityGroup(
            new PairedStats(MANY_VALUES_STATS_ITERABLE, MANY_VALUES_STATS_ITERABLE, 1.23))

                  * values.count();
    }
    yStats.addAll(values.yStats());
  }

  /** Returns an immutable snapshot of the current statistics. */
  public PairedStats snapshot() {
    return new PairedStats(xStats.snapshot(), yStats.snapshot(), sumOfProductsOfDeltas);
  }

  /** Returns the number of pairs in the dataset. */
  public long count() {
    return xStats.count();
  }

  static final PairedStats MANY_VALUES_PAIRED_STATS = buildManyValuesPairedStats();
  static final PairedStats DUPLICATE_MANY_VALUES_PAIRED_STATS =
      createPairedStatsOf(MANY_VALUES, OTHER_MANY_VALUES);
  static final PairedStats HORIZONTAL_VALUES_PAIRED_STATS = buildHorizontalValuesPairedStats();
  static final PairedStats VERTICAL_VALUES_PAIRED_STATS = buildVerticalValuesPairedStats();

 * {@link PairedStatsAccumulator#add}, and various error cases of that method. For tests of the
 * {@link PairedStatsAccumulator#snapshot} method which returns {@link PairedStats} instances, see
 * {@link PairedStatsTest}.
 *
 * @author Pete Gillin
 */
@NullUnmarked
public class PairedStatsAccumulatorTest extends TestCase {

  private PairedStatsAccumulator emptyAccumulator;