assertThat(network.adjacentEdges(E12)).containsExactlyElementsIn(adjacentEdges);
    }
  }

  @Override
  @Test
  public void edgesConnecting_checkReturnedSetMutability() {
    addNode(N1);
    addNode(N2);
    Set<String> edgesConnecting = network.edgesConnecting(N1, N2);
    UnsupportedOperationException e =
        assertThrows(UnsupportedOperationException.class, () -> edgesConnecting.add(E23));

        assertThrows(UnsupportedOperationException.class, () -> nodes.add(N2));
    addNode(N1);
    assertThat(graph.nodes()).containsExactlyElementsIn(nodes);
  }

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

    addNode(N1);
    Set<Integer> adjacentNodes = graph.adjacentNodes(N1);
    UnsupportedOperationException e =

  }

  @Test
  public void edgesConnecting_disconnectedNodes() {
    network.addNode(N1);
    network.addNode(N2);
    assertThat(networkForTest.edgesConnecting(N1, N2)).isEmpty();
  }

  @Test
  public void edgesConnecting_nodesNotInGraph() {
    network.addNode(N1);
    network.addNode(N2);
    IllegalArgumentException e =
        assertThrows(
            IllegalArgumentException.class,

    mutableNetwork.addNode("A");
    ImmutableNetwork<String, Integer> immutableNetwork = ImmutableNetwork.copyOf(mutableNetwork);

    assertThat(immutableNetwork.asGraph()).isInstanceOf(ImmutableGraph.class);
    assertThat(immutableNetwork).isNotInstanceOf(MutableNetwork.class);
    assertThat(immutableNetwork).isEqualTo(mutableNetwork);

    mutableNetwork.addNode("B");

     *
     * @return this {@code Builder} object
     */
    @CanIgnoreReturnValue
    public ImmutableValueGraph.Builder<N, V> addNode(N node) {
      mutableValueGraph.addNode(node);
      return this;
    }

    /**
     * Adds an edge connecting {@code nodeU} to {@code nodeV} if one is not already present, and

   */
  @CanIgnoreReturnValue
  boolean addNode(N node);

  /**
   * Adds an edge connecting {@code nodeU} to {@code nodeV} if one is not already present.
   *
   * <p>If the graph is directed, the resultant edge will be directed; otherwise, it will be
   * undirected.
   *
   * <p>If {@code nodeU} and {@code nodeV} are not already present in this graph, this method will

    return GraphBuilder.directed()
        .allowsSelfLoops(allowsSelfLoops)
        .incidentEdgeOrder(incidentEdgeOrder)
        .build();
  }

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

  @Override
  final void putEdge(Integer n1, Integer n2) {
    graphAsMutableGraph.putEdge(n1, n2);
  }

            .nodeOrder(nodeOrder)
            .edgeOrder(edgeOrder)
            .immutable();

    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();
  }

            .nodeOrder(nodeOrder)
            .edgeOrder(edgeOrder)
            .immutable();

    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();
  }

      NetworkBuilder.directed().<String, String>immutable().addNode("A").build();
  private static final ImmutableNetwork<String, String> IMMUTABLE_NETWORK_B =
      NetworkBuilder.directed().<String, String>immutable().addNode("B").build();

  public PackageSanityTests() {
    MutableNetwork<String, String> mutableNetworkA = NetworkBuilder.directed().build();
    mutableNetworkA.addNode("a");