public void set(E e) {
      throwIfInvalid(IteratorFeature.SUPPORTS_SET);

      stackWithLastReturnedElementAtTop.pop();
      stackWithLastReturnedElementAtTop.push(e);
    }

    /**
     * Moves the given element from its current position in {@link #nextElements} to the top of the
     * stack so that it is returned by the next call to {@link Iterator#next()}. If the element is

    public void set(E e) {
      throwIfInvalid(IteratorFeature.SUPPORTS_SET);

      stackWithLastReturnedElementAtTop.pop();
      stackWithLastReturnedElementAtTop.push(e);
    }

    /**
     * Moves the given element from its current position in {@link #nextElements} to the top of the
     * stack so that it is returned by the next call to {@link Iterator#next()}. If the element is

  @ParametricNullness
  private V getDoneValue(Object obj) throws ExecutionException {
    // While this seems like it might be too branch-y, simple benchmarking proves it to be
    // unmeasurable (comparing done AbstractFutures with immediateFuture)
    if (obj instanceof Cancellation) {
      throw cancellationExceptionWithCause("Task was cancelled.", ((Cancellation) obj).cause);

        (a, b) -> {
          count.incrementAndGet();
          assertThat(a.equals(String.valueOf(b))).isTrue();
        });
    assertThat(count.get()).isEqualTo(100000);
    // of course, this test doesn't prove that anything actually happened in parallel...
  }

  // TODO(kevinb): switch to importing Truth's assertThat(DoubleStream) if we get that added
  private static IterableSubject assertThatDoubleStream(DoubleStream stream) {

        verifyScenario(alteration.mutate(scenario), level + 1);
      }
    }
  }

  /**
   * An aggregation of an ordering with a list (of size > 1) that should prove to be in strictly
   * increasing order according to that ordering.
   */
  private static class Scenario<T extends @Nullable Object> {
    final Ordering<T> ordering;
    final List<T> strictlyOrderedList;

        verifyScenario(alteration.mutate(scenario), level + 1);
      }
    }
  }

  /**
   * An aggregation of an ordering with a list (of size > 1) that should prove to be in strictly
   * increasing order according to that ordering.
   */
  private static class Scenario<T extends @Nullable Object> {
    final Ordering<T> ordering;
    final List<T> strictlyOrderedList;

    assertEquals("bar", Iterables.getLast(iterable, "qux"));
  }

  /**
   * {@link ArrayList} extension that forbids the use of {@link Collection#iterator} for tests that
   * need to prove that it isn't called.
   */
  private static class DiesOnIteratorArrayList extends ArrayList<String> {
    /** @throws UnsupportedOperationException all the time */
    @Override
    public Iterator<String> iterator() {

    public int hashCode() {
      // Warning: this is broken if size() == 0, so it is critical that we
      // substitute an empty ImmutableSet to the user in place of this

      // It's a weird formula, but tests prove it works.
      int adjust = size() - 1;
      for (int i = 0; i < axes.size(); i++) {
        adjust *= 31;
        adjust = ~~adjust;
        // in GWT, we have to deal with integer overflow carefully
      }

      <name>Kevin Bourrillion</name>
      <email>******@****.***</email>
      <organization>Google</organization>
      <organizationUrl>http://www.google.com</organizationUrl>
      <roles>
        <role>owner</role>
        <role>developer</role>
      </roles>
      <timezone>-8</timezone>
    </developer>
  </developers>
  <ciManagement>
    <system>GitHub Actions</system>
    <url>https://github.com/google/guava/actions</url>

    assertEquals("bar", Iterables.getLast(iterable, "qux"));
  }

  /**
   * {@link ArrayList} extension that forbids the use of {@link Collection#iterator} for tests that
   * need to prove that it isn't called.
   */
  private static class DiesOnIteratorArrayList extends ArrayList<String> {
    /** @throws UnsupportedOperationException all the time */
    @Override
    public Iterator<String> iterator() {