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() {

    Iterator<E> iterator = collection.iterator();
    assertSetCount(e3(), 1);
    assertThrows(ConcurrentModificationException.class, iterator::next);
  }

  @CollectionFeature.Require({SUPPORTS_ADD, FAILS_FAST_ON_CONCURRENT_MODIFICATION})
  public void testSetCountZeroToOneConcurrentWithEntrySetIteration() {
    Iterator<Entry<E>> iterator = getMultiset().entrySet().iterator();

  @CollectionSize.Require(SEVERAL)
  public void testClearConcurrentWithIteration() {
    assertThrows(
        ConcurrentModificationException.class,
        () -> {
          Iterator<E> iterator = collection.iterator();
          collection.clear();
          iterator.next();
        });
  }

      return;
    }

    Set<Entry<K, V>> entrySet = map.entrySet();
    Iterator<Entry<K, V>> iterator = entrySet.iterator();
    if (supportsIteratorRemove) {
      int initialSize = map.size();
      Entry<K, V> entry = iterator.next();
      Entry<K, V> entryCopy = mapEntry(entry.getKey(), entry.getValue());

      iterator.remove();
      assertEquals(initialSize - 1, map.size());

import com.google.common.collect.testing.features.CollectionFeature;
import java.lang.reflect.Method;
import java.util.Iterator;
import java.util.List;
import org.jspecify.annotations.NullMarked;
import org.jspecify.annotations.Nullable;
import org.junit.Ignore;

/**
 * Tester to make sure the {@code iterator().remove()} implementation of {@code Multiset} works when
 * there are multiple occurrences of elements.
 *

      @Override
      SortedMultiset<E> forwardMultiset() {
        return AbstractSortedMultiset.this;
      }

      @Override
      Iterator<Entry<E>> entryIterator() {
        return descendingEntryIterator();
      }

      @Override
      public Iterator<E> iterator() {
        return descendingIterator();
      }
    }
    return new DescendingMultisetImpl();
  }

  /**
   * A sensible definition of {@link #firstEntry()} in terms of {@code entrySet().iterator()}.
   *
   * <p>If you override {@link #entrySet()}, you may wish to override {@link #firstEntry()} to
   * forward to this implementation.
   */
  protected @Nullable Entry<E> standardFirstEntry() {
    Iterator<Entry<E>> entryIterator = entrySet().iterator();
    if (!entryIterator.hasNext()) {
      return null;
    }

  public void testPutAbsentConcurrentWithEntrySetIteration() {
    assertThrows(
        ConcurrentModificationException.class,
        () -> {
          Iterator<Entry<K, V>> iterator = getMap().entrySet().iterator();
          put(e3());
          iterator.next();
        });
  }

  @MapFeature.Require({FAILS_FAST_ON_CONCURRENT_MODIFICATION, SUPPORTS_PUT})
  @CollectionSize.Require(absent = ZERO)