graph.addNode(3);
    graph.addNode(1);
    graph.addNode(4);
  }

  private static void addEdges(MutableNetwork<Integer, String> network) {
    network.addEdge(3, 1, "i");
    network.addEdge(1, 4, "e");
    network.addEdge(4, 3, "p");
  }

  private static class NonComparableSuperClass {
    final Integer value;

    NonComparableSuperClass(Integer value) {

  }

  @Test
  public void adjacentEdges_bothEndpoints() {
    addEdge(N1, N2, E12);
    addEdge(N2, N3, E23);
    addEdge(N3, N1, E31);
    addEdge(N3, N4, E34);
    assertThat(network.adjacentEdges(E12)).containsExactly(E31, E23);
  }

  @Test
  public void adjacentEdges_noAdjacentEdges() {
    addEdge(N1, N2, E12);
    addEdge(N3, N4, E34);
    assertThat(network.adjacentEdges(E12)).isEmpty();
  }

  }

  @Test
  public void adjacentEdges_bothEndpoints() {
    addEdge(N1, N2, E12);
    addEdge(N2, N3, E23);
    addEdge(N3, N1, E31);
    addEdge(N3, N4, E34);
    assertThat(network.adjacentEdges(E12)).containsExactly(E31, E23);
  }

  @Test
  public void adjacentEdges_noAdjacentEdges() {
    addEdge(N1, N2, E12);
    addEdge(N3, N4, E34);
    assertThat(network.adjacentEdges(E12)).isEmpty();
  }

        NetworkBuilder.directed().allowsSelfLoops(true).build();
    directedNetwork.addNode(N0);
    directedNetwork.addEdge(N1, N2, E12);
    directedNetwork.addEdge(N2, N1, E21);
    directedNetwork.addEdge(N1, N3, E13);
    directedNetwork.addEdge(N4, N4, E44);
    containsExactlySanityCheck(
        directedNetwork.asGraph().edges(),
        EndpointPair.ordered(N1, N2),

        NetworkBuilder.directed().allowsSelfLoops(true).build();
    directedNetwork.addNode(N0);
    directedNetwork.addEdge(N1, N2, E12);
    directedNetwork.addEdge(N2, N1, E21);
    directedNetwork.addEdge(N1, N3, E13);
    directedNetwork.addEdge(N4, N4, E44);
    containsExactlySanityCheck(
        directedNetwork.asGraph().edges(),
        EndpointPair.ordered(N1, N2),

  @Test
  public void edgesConnecting_parallelEdges() {
    network.addEdge(N1, N2, E12);
    network.addEdge(N1, N2, E12_A);
    network.addEdge(N2, N1, E21);
    if (edgeType == EdgeType.DIRECTED) {
      assertThat(networkForTest.edgesConnecting(N1, N2)).containsExactly(E12, E12_A);
      assertThat(networkForTest.edgesConnecting(N2, N1)).containsExactly(E21);
    } else {

    edgeToReferenceNode.put(edge, nodeU);
    return true;
  }

  @Override
  @CanIgnoreReturnValue
  public boolean addEdge(EndpointPair<N> endpoints, E edge) {
    validateEndpoints(endpoints);
    return addEdge(endpoints.nodeU(), endpoints.nodeV(), edge);
  }

  @Override
  @CanIgnoreReturnValue
  public boolean removeNode(N node) {
    checkNotNull(node, "node");

  }

  @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");

   *         .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();
   * }</pre>

    graph.addNode(3);
    graph.addNode(1);
    graph.addNode(4);
  }

  private static void addEdges(MutableNetwork<Integer, String> network) {
    network.addEdge(3, 1, "i");
    network.addEdge(1, 4, "e");
    network.addEdge(4, 3, "p");
  }

  private static class NonComparableSuperClass {
    final Integer value;

    NonComparableSuperClass(Integer value) {