addEdge(N1, N1, E11);
    addEdge(N1, N2, E12);
    assertThat(network.adjacentEdges(E11)).containsExactly(E12);
  }

  @Test
  public void edgesConnecting_selfLoop() {
    assume().that(network.allowsSelfLoops()).isTrue();

    addEdge(N1, N1, E11);
    assertThat(network.edgesConnecting(N1, N1)).containsExactly(E11);
    addEdge(N1, N2, E12);

    addEdge(N1, N1, E11);
    addEdge(N1, N2, E12);
    assertThat(network.adjacentEdges(E11)).containsExactly(E12);
  }

  @Test
  public void edgesConnecting_selfLoop() {
    assume().that(network.allowsSelfLoops()).isTrue();

    addEdge(N1, N1, E11);
    assertThat(network.edgesConnecting(N1, N1)).containsExactly(E11);
    addEdge(N1, N2, E12);

   *         .allowsParallelEdges(true)
   *         .<City, Train>immutable()
   *         .addEdge(PARIS, BRUSSELS, Thalys.trainNumber("1111"))
   *         .addEdge(PARIS, BRUSSELS, RegionalTrain.trainNumber("2222"))
   *         .addEdge(LONDON, PARIS, Eurostar.trainNumber("3333"))
   *         .addEdge(LONDON, BRUSSELS, Eurostar.trainNumber("4444"))
   *         .addNode(REYKJAVIK)
   *         .build();
   * }

  }

  @Test
  public void edgesConnecting_directed() {
    MutableNetwork<String, String> mutableNetwork =
        NetworkBuilder.directed().allowsSelfLoops(true).build();
    mutableNetwork.addEdge("A", "A", "AA");
    mutableNetwork.addEdge("A", "B", "AB");
    Network<String, String> network = ImmutableNetwork.copyOf(mutableNetwork);

    assertThat(network.edgesConnecting("A", "A")).containsExactly("AA");

    addEdge(N1, N1, E11);
    addEdge(N1, N2, E12);
    assertThat(network.adjacentNodes(N1)).containsExactly(N1, N2);
  }

  @Test
  public void adjacentEdges_selfLoop() {
    assume().that(network.allowsSelfLoops()).isTrue();

    addEdge(N1, N1, E11);
    addEdge(N1, N2, E12);
    assertThat(network.adjacentEdges(E11)).containsExactly(E12);
  }

  @Test

    // for ug1, add e12 first, then e12_a
    g1.addEdge(N1, N2, E12);
    g1.addEdge(N1, N2, E12_A);

    // for ug2, add e12_a first, then e12
    g2.addEdge(N1, N2, E12_A);
    g2.addEdge(N1, N2, E12);

    assertThat(g1).isEqualTo(g2);
  }

  @Test
  public void equivalent_edgeDirectionsDiffer() {
    network.addEdge(N1, N2, E12);

    // for ug1, add e12 first, then e12_a
    g1.addEdge(N1, N2, E12);
    g1.addEdge(N1, N2, E12_A);

    // for ug2, add e12_a first, then e12
    g2.addEdge(N1, N2, E12_A);
    g2.addEdge(N1, N2, E12);

    assertThat(g1).isEqualTo(g2);
  }

  @Test
  public void equivalent_edgeDirectionsDiffer() {
    network.addEdge(N1, N2, E12);

        .edgeOrder(edgeOrder)
        .build();
  }

  @Override
  void addNode(Integer n) {
    networkAsMutableNetwork.addNode(n);
  }

  @Override
  void addEdge(Integer n1, Integer n2, String e) {
    networkAsMutableNetwork.addEdge(n1, n2, e);
  }

    return networkBuilder.build();
  }

  @Override
  void addNode(Integer n) {
    networkBuilder.addNode(n);
    network = networkBuilder.build();
  }

  @Override
  void addEdge(Integer n1, Integer n2, String e) {
    networkBuilder.addEdge(n1, n2, e);
    network = networkBuilder.build();
  }

        {
            ArtifactMetadata md = node.getMd();
            MetadataGraphEdge e =
                    new MetadataGraphEdge(md.version, md.resolved, md.artifactScope, md.artifactUri, depth, pomOrder);
            addEdge(parentVertex, vertex, e);
        } else {
            entry = vertex;
        }

        MetadataTreeNode[] kids = node.getChildren();
        if (kids == null || kids.length < 1) {
            return;