ArrayList<Integer> nodeList = new ArrayList<>(network.nodes());
      for (int i = 0; i < NUM_EDGES; ++i) {
        // Parallel edges are allowed, so this should always succeed.
        assertThat(
                network.addEdge(
                    getRandomElement(nodeList, gen), getRandomElement(nodeList, gen), new Object()))
            .isTrue();
      }
      ArrayList<Object> edgeList = new ArrayList<>(network.edges());

        .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();
  }

    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();
  }

      ArrayList<Integer> nodeList = new ArrayList<>(network.nodes());
      for (int i = 0; i < NUM_EDGES; ++i) {
        // Parallel edges are allowed, so this should always succeed.
        assertThat(
                network.addEdge(
                    getRandomElement(nodeList, gen), getRandomElement(nodeList, gen), new Object()))
            .isTrue();
      }
      ArrayList<Object> edgeList = new ArrayList<>(network.edges());

    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

    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);

    directedGraph.addEdge(N1, N2, E12);
    directedGraph.addEdge(N1, N2, E12_A);
    directedGraph.addEdge(N1, N1, E11);
    directedGraph.addEdge(N3, N4, E34);

    MutableNetwork<Integer, String> expectedTranspose =
        NetworkBuilder.directed().allowsParallelEdges(true).allowsSelfLoops(true).build();
    expectedTranspose.addEdge(N3, N1, E13);
    expectedTranspose.addEdge(N1, N3, E31);
    expectedTranspose.addEdge(N2, N1, E12);

      network.addEdge(1, 2, "1-2a");
      network.addEdge(1, 2, "1-2b");
    }
    assertThat(hasCycle(directedNetwork)).isFalse();
    assertThat(hasCycle(undirectedNetwork)).isTrue(); // cyclic in undirected case
  }

  @Test
  public void hasCycle_cyclicMultigraph() {
    for (MutableNetwork<Integer, String> network : networksToTest) {
      network.addEdge(1, 2, "1-2a");

    MutableNetwork<String, Integer> network = NetworkBuilder.directed().build();
    network.addEdge("a", "b", 11);

    Traverser.forTree(network); // Does not throw
  }

  @Test
  public void forTree_withUndirectedNetwork_throws() throws Exception {
    MutableNetwork<String, Integer> network = NetworkBuilder.undirected().build();
    network.addEdge("a", "b", 11);