}
          horizon.removeFirst();
          return null;
        }
      };
    }

    final Iterator<N> breadthFirst(Iterator<? extends N> startNodes) {
      return topDown(startNodes, InsertionOrder.BACK);
    }

    final Iterator<N> preOrder(Iterator<? extends N> startNodes) {
      return topDown(startNodes, InsertionOrder.FRONT);
    }

    /**

import java.io.Serializable;
import org.jspecify.annotations.Nullable;

/** An ordering that uses the natural order of the values. */
@GwtCompatible
final class NaturalOrdering extends Ordering<Comparable<?>> implements Serializable {
  static final NaturalOrdering INSTANCE = new NaturalOrdering();

  /*
   * TODO: b/287198172 - Consider eagerly initializing these, maybe making them static. But that

  }

  /** Runs sanity tests against return values of static factory methods declared by a class. */
  public final class FactoryMethodReturnValueTester {
    private final Set<String> packagesToTest = new HashSet<>();
    private final Class<?> declaringClass;
    private final ImmutableList<Invokable<?, ?>> factories;
    private final String factoryMethodsDescription;
    private Class<?> returnTypeToTest = Object.class;

 * @author koichik
 *
 */
public class MultiIteratorTest {

    /**
     *
     */
    @Test
    public void test() {
        final List<String> list1 = asList("Foo", "Bar");
        final List<String> list2 = asList("Baz");

        @SuppressWarnings("unchecked")
        final Iterator<String> it = new MultiIterator<String>(list1.iterator(), list2.iterator());

        assertThat(it.hasNext(), is(true));

/**
 * Test case for {@link EventBus}.
 *
 * @author Cliff Biffle
 */
@NullUnmarked
public class EventBusTest extends TestCase {
  private static final String EVENT = "Hello";
  private static final String BUS_IDENTIFIER = "test-bus";

  private EventBus bus;

  @Override
  protected void setUp() throws Exception {
    super.setUp();
    bus = new EventBus(BUS_IDENTIFIER);
  }

   *
   * <p>We use this instead of java.util.BitSet because we need access to the array of longs and we
   * need compare-and-swap.
   */
  static final class LockFreeBitArray {
    private static final int LONG_ADDRESSABLE_BITS = 6;
    final AtomicLongArray data;
    private final LongAddable bitCount;

    LockFreeBitArray(long bits) {
      checkArgument(bits > 0, "data length is zero!");

/**
 * Test case for {@link EventBus}.
 *
 * @author Cliff Biffle
 */
@NullUnmarked
public class EventBusTest extends TestCase {
  private static final String EVENT = "Hello";
  private static final String BUS_IDENTIFIER = "test-bus";

  private EventBus bus;

  @Override
  protected void setUp() throws Exception {
    super.setUp();
    bus = new EventBus(BUS_IDENTIFIER);
  }

   *
   * <p>Example:
   *
   * {@snippet :
   * static final Multimap<Character, String> FIRST_LETTER_MULTIMAP =
   *     Stream.of("banana", "apple", "carrot", "asparagus", "cherry")
   *         .collect(toImmutableSetMultimap(str -> str.charAt(0), str -> str.substring(1)));
   *
   * // is equivalent to
   *
   * static final Multimap<Character, String> FIRST_LETTER_MULTIMAP =

     */
    private static class StringItem implements Item {
        private static final List<String> QUALIFIERS =
                Arrays.asList("alpha", "beta", "milestone", "rc", "snapshot", "", "sp");
        private static final List<String> RELEASE_QUALIFIERS = Arrays.asList("ga", "final", "release");

        private static final Properties ALIASES = new Properties();

        static {
            ALIASES.put("cr", "rc");

   *     simple statement {@code return endOfData();}
   */
  @CanIgnoreReturnValue
  protected final @Nullable T endOfData() {
    state = State.DONE;
    return null;
  }

  @Override
  public final boolean hasNext() {
    checkState(state != State.FAILED);
    switch (state) {
      case DONE:
        return false;
      case READY: