}

  @Override
  @Test
  public void edges_checkReturnedSetMutability() {
    assume().that(graphIsMutable()).isTrue();

    Set<String> edges = network.edges();
    UnsupportedOperationException e =
        assertThrows(UnsupportedOperationException.class, () -> edges.add(E12));
    addEdge(N1, N2, E12);
    assertThat(network.edges()).containsExactlyElementsIn(edges);
  }

  @Override
  @Test

 *   <li>graphs whose nodes/edges are insertion-ordered, sorted, or unordered
 *   <li>graphs whose edges have associated values
 * </ul>
 *
 * <p>{@code ValueGraph}, as a subtype of {@code Graph}, explicitly does not support parallel edges,
 * and forbids implementations or extensions with parallel edges. If you need parallel edges, use
 * {@link Network}. (You can use a positive {@code Integer} edge value as a loose representation of

  // Ideally, the ordering in test should never be updated.
  @Test
  public void stableIncidentEdgeOrder_edges_returnsInStableOrder() {
    assume().that(graph.incidentEdgeOrder().type()).isEqualTo(ElementOrder.Type.STABLE);

    populateStarShapedGraph();

    assertThat(graph.edges())
        .containsExactly(
            EndpointPair.ordered(2, 1),
            EndpointPair.ordered(1, 4),

    assertThat(e.getMessage()).contains(ERROR_PARALLEL_EDGE);
    e = assertThrows(IllegalArgumentException.class, () -> undirectedGraph.addEdge(N2, N1, E21));
    assertThat(e.getMessage()).contains(ERROR_PARALLEL_EDGE);

    // By default, self-loop edges are not allowed.
    e = assertThrows(IllegalArgumentException.class, () -> undirectedGraph.addEdge(N1, N1, E11));

          assertThat(graph.hasEdgeConnecting(endpoints.nodeU(), endpoints.nodeV())).isTrue();
        }
      }
    }

    sanityCheckSet(graph.edges());
    assertThat(graph.edges()).doesNotContain(EndpointPair.of(graph, new Object(), new Object()));
    assertThat(graph.edges()).isEqualTo(allEndpointPairs);
  }

  /**
   * Verifies that the {@code Set} returned by {@code nodes} has the expected mutability property

        while (resultWithDoubleSelfLoop.hasNext()) {
          EndpointPair<N> edge = resultWithDoubleSelfLoop.next();
          if (edge.nodeU().equals(edge.nodeV())) {
            if (!alreadySeenSelfLoop.getAndSet(true)) {
              return edge;
            }
          } else {
            return edge;
          }
        }
        return endOfData();
      }
    };
  }

            throw new MetadataResolutionException("badly formed edge");
        }
    }
    // ------------------------------------------------------------------------
    public List<MetadataGraphEdge> getEdgesBetween(MetadataGraphVertex vFrom, MetadataGraphVertex vTo) {
        List<MetadataGraphEdge> edges = getIncidentEdges(vTo);
        if (edges == null || edges.isEmpty()) {
            return null;
        }

          "stanford.edu",
          "state.ca.us",
          "www.state.ca.us",
          "state.ca.us",
          "pvt.k12.ca.us",
          "www.rave.ca.",
          "cnn.ca",
          "ledger-enquirer.com",
          "it-trace.ch",
          "cool.dk",
          "cool.co.uk",
          "cool.de",
          "cool.es",
          "cool\uFF61fr", // Alternate dot character
          "cool.nl",

        ComparableVersion version2 = new ComparableVersion("0.2");
        assertEquals("0.2", version2.getCanonical());
    }

    /**
     * Test <a href="https://issues.apache.org/jira/browse/MNG-5568">MNG-5568</a> edge case
     * which was showing transitive inconsistency: since A &gt; B and B &gt; C then we should have A &gt; C
     * otherwise sorting a list of ComparableVersions() will in some cases throw runtime exception;

 * </ul>
 *
 * @author Jens Nyman
 * @param <N> Node parameter type
 * @since 23.1
 */
@Beta
@DoNotMock(
    "Call forGraph or forTree, passing a lambda or a Graph with the desired edges (built with"
        + " GraphBuilder)")
@ElementTypesAreNonnullByDefault
public abstract class Traverser<N> {
  private final SuccessorsFunction<N> successorFunction;