assertThat(hasCycle(undirectedGraph)).isFalse();
  }

  @Test
  public void hasCycle_isolatedNodes() {
    for (MutableGraph<Integer> graph : graphsToTest) {
      graph.addNode(1);
      graph.addNode(2);
    }
    assertThat(hasCycle(directedGraph)).isFalse();
    assertThat(hasCycle(undirectedGraph)).isFalse();
  }

  @Test
  public void hasCycle_oneEdge() {

   * <p><b>Nodes must be unique</b>, just as {@code Map} keys must be. They must also be non-null.
   *
   * @return {@code true} if the network was modified as a result of this call
   */
  @CanIgnoreReturnValue
  boolean addNode(N node);

  /**
   * Adds {@code edge} connecting {@code nodeU} to {@code nodeV}.
   *
   * <p>If the graph is directed, {@code edge} will be directed in this graph; otherwise, it will be
   * undirected.
   *

      assertThat(network.nodes()).isEmpty();
      assertThat(network.edges()).isEmpty();
      AbstractNetworkTest.validateNetwork(network);

      while (network.nodes().size() < NUM_NODES) {
        network.addNode(gen.nextInt(NODE_POOL_SIZE));
      }
      ArrayList<Integer> nodeList = new ArrayList<>(network.nodes());
      for (int i = 0; i < NUM_EDGES; ++i) {
        // Parallel edges are allowed, so this should always succeed.

    }
    throw new IllegalStateException("Unexpected edge type: " + edgeType);
  }

  @Test
  public void equivalent_nodeSetsDiffer() {
    network.addNode(N1);

    MutableNetwork<Integer, String> g2 = createNetwork(edgeType);
    g2.addNode(N2);

    assertThat(network).isNotEqualTo(g2);
  }

  // Node sets are the same, but edge sets differ.
  @Test
  public void equivalent_edgeSetsDiffer() {

    }
    throw new IllegalStateException("Unexpected edge type: " + edgeType);
  }

  @Test
  public void equivalent_nodeSetsDiffer() {
    network.addNode(N1);

    MutableNetwork<Integer, String> g2 = createNetwork(edgeType);
    g2.addNode(N2);

    assertThat(network).isNotEqualTo(g2);
  }

  // Node sets are the same, but edge sets differ.
  @Test
  public void equivalent_edgeSetsDiffer() {

   * element, or at the end of the list if {@code nextSibling} is null. Note: if {@code nextSibling}
   * is specified, it MUST be for a node for the same {@code key}!
   */
  @CanIgnoreReturnValue
  private Node<K, V> addNode(
      @ParametricNullness K key,
      @ParametricNullness V value,
      @CheckForNull Node<K, V> nextSibling) {
    Node<K, V> node = new Node<>(key, value);
    if (head == null) { // empty list

  StandardMutableNetwork(NetworkBuilder<? super N, ? super E> builder) {
    super(builder);
  }

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

    if (containsNode(node)) {
      return false;
    }

    addNodeInternal(node);
    return true;
  }

  /**

    MutableGraph<Integer> directedGraph = GraphBuilder.directed().allowsSelfLoops(false).build();
    directedGraph.putEdge(N1, N2);
    directedGraph.putEdge(N1, N3);
    directedGraph.putEdge(N2, N3);
    directedGraph.addNode(N4);

    MutableGraph<Integer> expectedClosure = GraphBuilder.directed().allowsSelfLoops(true).build();
    expectedClosure.putEdge(N1, N1);
    expectedClosure.putEdge(N1, N2);
    expectedClosure.putEdge(N1, N3);

      }
    };
  }

  private static ImmutableGraph<Character> createSingleRootGraph() {
    MutableGraph<Character> graph = GraphBuilder.directed().build();
    graph.addNode('a');
    return ImmutableGraph.copyOf(graph);
  }

  private static void assertEqualCharNodes(Iterable<Character> result, String expectedCharacters) {
    assertThat(ImmutableList.copyOf(result))

      }
    };
  }

  private static ImmutableGraph<Character> createSingleRootGraph() {
    MutableGraph<Character> graph = GraphBuilder.directed().build();
    graph.addNode('a');
    return ImmutableGraph.copyOf(graph);
  }

  private static void assertEqualCharNodes(Iterable<Character> result, String expectedCharacters) {
    assertThat(ImmutableList.copyOf(result))