* directly against {@code equals()} rather than through the {@code Equivalence}.
   */
  private final Equivalence<? super T> equivalence;

  private final String relationshipName;
  private final String hashName;
  private final ItemReporter itemReporter;
  private final List<ImmutableList<T>> groups = new ArrayList<>();

  RelationshipTester(
      Equivalence<? super T> equivalence,
      String relationshipName,
      String hashName,

       * since the Equivalence base type now implements this logic itself
       */
      assertTrue(item + " must be inequivalent to null", !equivalence.equivalent(item, null));
      assertTrue("null must be inequivalent to " + item, !equivalence.equivalent(null, item));
      assertTrue(item + " must be equivalent to itself", equivalence.equivalent(item, item));
      assertEquals(

   * directly against {@code equals()} rather than through the {@code Equivalence}.
   */
  private final Equivalence<? super T> equivalence;

  private final String relationshipName;
  private final String hashName;
  private final ItemReporter itemReporter;
  private final List<ImmutableList<T>> groups = new ArrayList<>();

  RelationshipTester(
      Equivalence<? super T> equivalence,
      String relationshipName,
      String hashName,

  private final Equivalence<T> resultEquivalence;

  FunctionalEquivalence(
      Function<? super F, ? extends @Nullable T> function, Equivalence<T> resultEquivalence) {
    this.function = checkNotNull(function);
    this.resultEquivalence = checkNotNull(resultEquivalence);
  }

  @Override
  protected boolean doEquivalent(F a, F b) {
    return resultEquivalence.equivalent(function.apply(a), function.apply(b));
  }

        .addEquivalenceGroup("a")
        .test();
  }

  public void testEquals() {
    new EqualsTester()
        .addEqualityGroup(Equivalence.equals(), Equivalence.equals())
        .addEqualityGroup(Equivalence.identity(), Equivalence.identity())
        .testEquals();
  }

  @J2ktIncompatible
  @GwtIncompatible // NullPointerTester
  public void testNulls() throws NoSuchMethodException {

        .addEquivalenceGroup("a")
        .test();
  }

  public void testEquals() {
    new EqualsTester()
        .addEqualityGroup(Equivalence.equals(), Equivalence.equals())
        .addEqualityGroup(Equivalence.identity(), Equivalence.identity())
        .testEquals();
  }

  @J2ktIncompatible
  @GwtIncompatible // NullPointerTester
  public void testNulls() throws NoSuchMethodException {

  private CollectorTester(
      Collector<T, A, R> collector, BiPredicate<? super R, ? super R> equivalence) {
    this.collector = checkNotNull(collector);
    this.equivalence = checkNotNull(equivalence);
  }

  /**
   * Different orderings for combining the elements of an input array, which must all produce the
   * same result.
   */

  private CollectorTester(
      Collector<T, A, R> collector, BiPredicate<? super R, ? super R> equivalence) {
    this.collector = checkNotNull(collector);
    this.equivalence = checkNotNull(equivalence);
  }

  /**
   * Different orderings for combining the elements of an input array, which must all produce the
   * same result.
   */
  enum CollectStrategy {

        toImmutableEnumMap(Entry::getKey, Entry::getValue);
    Equivalence<ImmutableMap<AnEnum, Integer>> equivalence =
        Equivalence.equals().<Entry<AnEnum, Integer>>pairwise().onResultOf(ImmutableMap::entrySet);
    CollectorTester.of(collector, equivalence)
        .expectCollects(
            ImmutableMap.of(AnEnum.A, 1, AnEnum.C, 2, AnEnum.E, 3),

import java.util.Iterator;
import org.jspecify.annotations.Nullable;

@GwtCompatible
final class PairwiseEquivalence<E, T extends @Nullable E> extends Equivalence<Iterable<T>>
    implements Serializable {
  final Equivalence<E> elementEquivalence;

  PairwiseEquivalence(Equivalence<E> elementEquivalence) {
    this.elementEquivalence = Preconditions.checkNotNull(elementEquivalence);
  }

  @Override