totalSize -= collection.size();
    collection.clear();

    return unmodifiableCollectionSubclass(output);
  }

  <E extends @Nullable Object> Collection<E> unmodifiableCollectionSubclass(
      Collection<E> collection) {
    return Collections.unmodifiableCollection(collection);
  }

  @Override
  public void clear() {
    // Clear each collection, to make previously returned collections empty.

public class MultisetEntrySetTester<E> extends AbstractMultisetTester<E> {

  @CollectionFeature.Require(SUPPORTS_REMOVE)
  public void testEntrySet_clear() {
    getMultiset().entrySet().clear();
    assertTrue("multiset not empty after entrySet().clear()", getMultiset().isEmpty());
  }

  @CollectionSize.Require(ONE)
  @CollectionFeature.Require(SUPPORTS_ITERATOR_REMOVE)
  public void testEntrySet_iteratorRemovePropagates() {

## Contributing

When adding new tests:
1. Follow the existing naming convention: `test_<method>_<scenario>_<expectedResult>`
2. Add clear JavaDoc comments explaining the test purpose
3. Ensure tests are independent and can run in any order
4. Clean up resources in finally blocks or use try-with-resources

    assertMultimapRemainsUnmodified(multimap, originalEntries);

    Collection<V> sampleValueAsCollection = singleton(sampleValue);

    // Test #clear()
    try {
      multimap.clear();
      fail("clear succeeded on unmodifiable multimap");
    } catch (UnsupportedOperationException expected) {
    }

    assertMultimapRemainsUnmodified(multimap, originalEntries);

 * https://github.com/google/guava/issues/3990
 */
@J2ktIncompatible
@GwtIncompatible
final class Java8Compatibility {
  static void clear(Buffer b) {
    b.clear();
  }

  static void flip(Buffer b) {
    b.flip();
  }

  static void limit(Buffer b, int limit) {
    b.limit(limit);
  }

  static void position(Buffer b, int position) {

 * https://github.com/google/guava/issues/3990
 */
@J2ktIncompatible
@GwtIncompatible
final class Java8Compatibility {
  static void clear(Buffer b) {
    b.clear();
  }

  static void flip(Buffer b) {
    b.flip();
  }

  static void limit(Buffer b, int limit) {
    b.limit(limit);
  }

  static void position(Buffer b, int position) {

    public boolean remove(final Object o) {
        return map.remove(o) == PRESENT;
    }

    /**
     * Removes all of the elements from this set.
     */
    @Override
    public void clear() {
        map.clear();
    }

  @BeforeExperiment
  protected void setUp() {
    BitSet bitSet = new BitSet();
    for (int i = 0; i < OLD_WHITESPACE_TABLE.length(); i++) {
      bitSet.set(OLD_WHITESPACE_TABLE.charAt(i));
    }
    bitSet.clear(0);
    bitSet.clear(1);
    matcher = useNew ? CharMatcher.whitespace() : OLD_WHITESPACE;
    teststring = newTestString(new Random(1), bitSet, percentMatching);
  }

  @Benchmark
  public int countIn(int reps) {

/**
 * Wrappers around {@link Buffer} methods that are covariantly overridden in Java 9+. See
 * https://github.com/google/guava/issues/3990
 */
@GwtIncompatible
final class Java8Compatibility {
  static void clear(Buffer b) {
    b.clear();
  }

  static void flip(Buffer b) {
    b.flip();
  }

  static void limit(Buffer b, int limit) {
    b.limit(limit);
  }

  static void position(Buffer b, int position) {

 * https://github.com/google/guava/issues/3990
 */
@J2ktIncompatible
@GwtIncompatible
final class Java8Compatibility {
  static void clear(Buffer b) {
    b.clear();
  }

  static void flip(Buffer b) {
    b.flip();
  }

  static void limit(Buffer b, int limit) {
    b.limit(limit);
  }

  static void mark(Buffer b) {
    b.mark();
  }