* while iteration is in progress.
   *
   * <p>The returned {@code Iterable} can be iterated over multiple times. Every iterator will
   * compute its next element on the fly. It is thus possible to limit the traversal to a certain
   * number of nodes as follows:
   *
   * <pre>{@code
   * Iterables.limit(Traverser.forGraph(graph).breadthFirst(node), maxNumberOfNodes);
   * }</pre>
   *

import org.eclipse.aether.metadata.Metadata;
import org.eclipse.aether.util.ConfigUtils;

/**
 * Maven remote GAV level metadata generator.
 * <p>
 * Remote snapshot metadata converts artifact on-the-fly to use timestamped snapshot version, and enlist it accordingly.
 */
class RemoteSnapshotMetadataGenerator implements MetadataGenerator {

    private final Map<Object, RemoteSnapshotMetadata> snapshots;

     *   lock.lock();
     * }
     * operation();
     * for (Lock lock : locks) {
     *   lock.unlock();
     * }
     *
     * If we only held the int[] stripes, translating it on the fly to L's, the original locks might
     * be garbage collected after locking them, ending up in a huge mess.
     */
    @SuppressWarnings("unchecked") // we carefully replaced all keys with their respective L's

    assertThrows(
        IllegalArgumentException.class,
        () -> Traverser.forGraph(createDirectedGraph()).breadthFirst('a'));
  }

  /**
   * Checks that the elements of the iterable are calculated on the fly. Concretely, that means that
   * {@link SuccessorsFunction#successors(Object)} can only be called for a subset of all nodes.
   */
  @Test
  public void forGraph_breadthFirstIterable_emptyGraph() {

    assertThrows(
        IllegalArgumentException.class,
        () -> Traverser.forGraph(createDirectedGraph()).breadthFirst('a'));
  }

  /**
   * Checks that the elements of the iterable are calculated on the fly. Concretely, that means that
   * {@link SuccessorsFunction#successors(Object)} can only be called for a subset of all nodes.
   */
  @Test
  public void forGraph_breadthFirstIterable_emptyGraph() {