* @author George van den Driessche
 */
@GwtCompatible
@NullMarked
public class AbstractTester<G> extends TestCase {
  private G subjectGenerator;
  private String suiteName;
  private @Nullable Runnable setUp;
  private @Nullable Runnable tearDown;

  // public so that it can be referenced in generated GWT tests.
  @Override
  public void setUp() throws Exception {
    if (setUp != null) {
      setUp.run();
    }
  }

 * @author George van den Driessche
 */
@GwtCompatible
@NullMarked
public class AbstractTester<G> extends TestCase {
  private G subjectGenerator;
  private String suiteName;
  private @Nullable Runnable setUp;
  private @Nullable Runnable tearDown;

  // public so that it can be referenced in generated GWT tests.
  @Override
  public void setUp() throws Exception {
    if (setUp != null) {
      setUp.run();
    }
  }

    return (Collector) TO_OPTIONAL;
  }

  private static final Object NULL_PLACEHOLDER = new Object();

  private static final Collector<@Nullable Object, ?, @Nullable Object> ONLY_ELEMENT =
      Collector.<@Nullable Object, ToOptionalState<Object>, @Nullable Object>of(
          () -> new ToOptionalState<>(null),
          (state, o) -> state.add((o == null) ? NULL_PLACEHOLDER : o),
          ToOptionalState::combine,

  private final boolean hasLowerBound;
  private final @Nullable T lowerEndpoint;
  private final BoundType lowerBoundType;
  private final boolean hasUpperBound;
  private final @Nullable T upperEndpoint;
  private final BoundType upperBoundType;

  private GeneralRange(
      Comparator<? super T> comparator,
      boolean hasLowerBound,
      @Nullable T lowerEndpoint,
      BoundType lowerBoundType,

   *
   * <p>The serialized output consists of the number of entries, first key, first value, second key,
   * second value, and so on.
   */
  static <K extends @Nullable Object, V extends @Nullable Object> void writeMap(
      Map<K, V> map, ObjectOutputStream stream) throws IOException {
    stream.writeInt(map.size());
    for (Map.Entry<K, V> entry : map.entrySet()) {

    static final Listener TOMBSTONE = new Listener();
    // null only for TOMBSTONE
    final @Nullable Runnable task;
    // null only for TOMBSTONE
    final @Nullable Executor executor;

    // writes to next are made visible by subsequent CAS's on the listeners field
    @Nullable Listener next;

    Listener(Runnable task, Executor executor) {
      this.task = task;
      this.executor = executor;

  @CanIgnoreReturnValue
  @Override
  public @Nullable V remove(@Nullable Object key) {
    return delegate().remove(key);
  }

  @Override
  public void clear() {
    delegate().clear();
  }

  @Override
  public boolean containsKey(@Nullable Object key) {
    return delegate().containsKey(key);
  }

  @Override
  public boolean containsValue(@Nullable Object value) {
    return delegate().containsValue(value);

import org.jspecify.annotations.Nullable;

/**
 * Derived suite generators for Guava collection interfaces, split out of the suite builders so that
 * they are available to GWT.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
@NullMarked
public final class DerivedGoogleCollectionGenerators {
  public static class MapGenerator<K extends @Nullable Object, V extends @Nullable Object>

      assertTrue(Thread.holdsLock(mutex));
      return delegate.removeLast();
    }

    @Override
    public @Nullable E pollFirst() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.pollFirst();
    }

    @Override
    public @Nullable E pollLast() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.pollLast();
    }

    @Override

  public void testTransformEntrySetContains() {
    Map<@Nullable String, @Nullable Boolean> underlying = new HashMap<>();
    underlying.put("a", null);
    underlying.put("b", true);
    underlying.put(null, true);

    Map<@Nullable String, @Nullable Boolean> map =
        transformValues(
            underlying,
            new Function<@Nullable Boolean, @Nullable Boolean>() {
              @Override