* non-null objects {@code x} and {@code y}, {@code equivalence.onResultOf(function).equivalent(a,
   * b)} is true if and only if {@code equivalence.equivalent(function.apply(a), function.apply(b))}
   * is true.
   *
   * <p>For example:
   *
   * {@snippet :
   * Equivalence<Person> SAME_AGE = Equivalence.equals().onResultOf(GET_PERSON_AGE);
   * }
   *

            comparator, DECREASING_INTEGER.onResultOf(StringLengthFunction.STRING_LENGTH))
        .addEqualityGroup(DECREASING_INTEGER.onResultOf(Functions.constant(1)))
        .addEqualityGroup(Ordering.natural())
        .testEquals();
    reserializeAndAssert(comparator);
    assertThat(comparator.toString())
        .isEqualTo("Ordering.natural().reverse().onResultOf(STRING_LENGTH)");
  }

            comparator, DECREASING_INTEGER.onResultOf(StringLengthFunction.STRING_LENGTH))
        .addEqualityGroup(DECREASING_INTEGER.onResultOf(Functions.constant(1)))
        .addEqualityGroup(Ordering.natural())
        .testEquals();
    reserializeAndAssert(comparator);
    assertThat(comparator.toString())
        .isEqualTo("Ordering.natural().reverse().onResultOf(STRING_LENGTH)");
  }

    BiPredicate<ImmutableSortedMap<String, Integer>, ImmutableSortedMap<String, Integer>>
        equivalence =
            Equivalence.equals()
                .onResultOf(ImmutableSortedMap<String, Integer>::comparator)
                .and(Equivalence.equals().onResultOf(map -> map.entrySet().asList()))
                .and(Equivalence.equals());
    ImmutableSortedMap<String, Integer> expected =

   *
   * {@snippet :
   * Ordering.from(String.CASE_INSENSITIVE_ORDER).onResultOf(Functions.toStringFunction())
   * }
   *
   * <p><b>Java 8+ users:</b> Use {@code Comparator.comparing(function, thisComparator)} instead
   * (you can omit the comparator if it is the natural order).
   */
  public <F extends @Nullable Object> Ordering<F> onResultOf(Function<F, ? extends T> function) {
    return new ByFunctionOrdering<>(function, this);

   *
   * {@snippet :
   * Ordering.from(String.CASE_INSENSITIVE_ORDER).onResultOf(Functions.toStringFunction())
   * }
   *
   * <p><b>Java 8+ users:</b> Use {@code Comparator.comparing(function, thisComparator)} instead
   * (you can omit the comparator if it is the natural order).
   */
  public <F extends @Nullable Object> Ordering<F> onResultOf(Function<F, ? extends T> function) {
    return new ByFunctionOrdering<>(function, this);

        toImmutableSetMultimap(Entry::getKey, Entry::getValue);
    BiPredicate<ImmutableSetMultimap<?, ?>, ImmutableSetMultimap<?, ?>> equivalence =
        Equivalence.equals()
            .onResultOf(
                (ImmutableSetMultimap<?, ?> mm) ->
                    ImmutableListMultimap.copyOf(mm).asMap().entrySet().asList())
            .and(Equivalence.equals());
    CollectorTester.of(collector, equivalence)

  }

  public void testToImmutableSet() {
    Collector<String, ?, ImmutableSet<String>> collector = toImmutableSet();
    Equivalence<ImmutableSet<String>> equivalence =
        Equivalence.equals().onResultOf(ImmutableSet::asList);
    CollectorTester.of(collector, equivalence)
        .expectCollects(ImmutableSet.of("a", "b", "c", "d"), "a", "b", "a", "c", "b", "b", "d");
  }

    assertEquals(HashMultiset.create(asList("a")), multiset);
  }

  public void testCreation_arrayOfArray() {
    Comparator<String[]> comparator =
        Ordering.natural().lexicographical().onResultOf(Arrays::asList);
    String[] array = new String[] {"a"};
    Multiset<String[]> multiset = ImmutableSortedMultiset.orderedBy(comparator).add(array).build();
    Multiset<String[]> expected = HashMultiset.create();

      return buildOrThrow();
    }

    private ImmutableMap<K, V> build(boolean throwIfDuplicateKeys) {
      if (valueComparator != null) {
        Collections.sort(entries, Ordering.from(valueComparator).onResultOf(Entry::getValue));
      }
      return fromEntryList(throwIfDuplicateKeys, entries);
    }

    public ImmutableMap<K, V> buildOrThrow() {
      return build(/* throwIfDuplicateKeys= */ true);
    }