}

  /**
   * A sensible definition of {@link #pollFirst} in terms of the {@code iterator} method. If you
   * override {@link #iterator} you may wish to override {@link #pollFirst} to forward to this
   * implementation.
   */
  protected @Nullable E standardPollFirst() {
    return Iterators.pollNext(iterator());
  }

  @Override
  public @Nullable E pollLast() {
    return delegate().pollLast();

    }
    try {
      Iterator<Integer> iterator = unmod.iterator();
      iterator.next();
      iterator.remove();
      fail("UnsupportedOperationException expected");
    } catch (UnsupportedOperationException expected) {
    }
    try {
      Iterator<Integer> iterator = unmod.descendingIterator();
      iterator.next();
      iterator.remove();

    public E element() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.element();
    }

    @Override
    public Iterator<E> iterator() {
      // We explicitly don't lock for iterator()
      assertFalse(Thread.holdsLock(mutex));
      return delegate.iterator();
    }

    @Override
    public int size() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.size();
    }

  public void testRemoveIfSomeMatchesConcurrentWithIteration() {
    assertThrows(
        ConcurrentModificationException.class,
        () -> {
          Iterator<E> iterator = collection.iterator();
          assertTrue(collection.removeIf(Predicate.isEqual(samples.e0())));
          iterator.next();
        });
  }

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

  public void testRemoveAtIndexConcurrentWithIteration() {
    assertThrows(
        ConcurrentModificationException.class,
        () -> {
          Iterator<E> iterator = collection.iterator();
          getList().remove(getNumElements() / 2);
          iterator.next();
        });
  }

  @ListFeature.Require(SUPPORTS_REMOVE_WITH_INDEX)
  @CollectionSize.Require(absent = ZERO)
  public void testRemoveAtIndex_last() {

        @Override
        public @Nullable Object execute(Iterator<?> iterator) {
          iterator.remove();
          return null;
        }
      };

  private static final IteratorOperation NEXT_METHOD =
      new IteratorOperation() {
        @Override
        public @Nullable Object execute(Iterator<?> iterator) {
          return iterator.next();
        }
      };

  }

  protected K getKeyForNullValue() {
    return getEntryNullReplaces().getKey();
  }

  private Entry<K, V> getEntryNullReplaces() {
    Iterator<Entry<K, V>> entries = getSampleElements().iterator();
    for (int i = 0; i < getNullLocation(); i++) {
      entries.next();
    }
    return entries.next();
  }

  /**

    assertThrows(NoSuchElementException.class, () -> iterator.next());
    assertThrows(IllegalStateException.class, () -> iterable.iterator());
  }

  public void testOf_one() {
    Iterable<String> iterable = MinimalIterable.of("a");
    Iterator<String> iterator = iterable.iterator();
    assertTrue(iterator.hasNext());
    assertEquals("a", iterator.next());
    assertFalse(iterator.hasNext());

      @Override
      public Iterator<T> iterator() {
        if (iterable instanceof List) {
          List<T> list = (List<T>) iterable;
          int toSkip = Math.min(list.size(), numberToSkip);
          return list.subList(toSkip, list.size()).iterator();
        }
        Iterator<T> iterator = iterable.iterator();

        Iterators.advance(iterator, numberToSkip);

        /*

      @Override
      protected Iterator<E> newTargetIterator() {
        resetCollection();
        return collection.iterator();
      }

      @Override
      protected void verify(List<E> elements) {
        expectContents(elements);
      }
    }.test();
  }

  public void testIteratorNoSuchElementException() {
    Iterator<E> iterator = collection.iterator();
    while (iterator.hasNext()) {