assertThat(e).hasMessageThat().contains(ERROR_REUSE_EDGE);
  }

  @Test
  public void addEdge_parallelEdge_notAllowed() {
    assume().that(graphIsMutable()).isTrue();
    assume().that(network.allowsParallelEdges()).isFalse();

    addEdge(N1, N2, E12);
    IllegalArgumentException e =
        assertThrows(
            IllegalArgumentException.class,

    assertThat(e).hasMessageThat().contains(ERROR_REUSE_EDGE);
  }

  @Test
  public void addEdge_parallelEdge_notAllowed() {
    assume().that(graphIsMutable()).isTrue();
    assume().that(network.allowsParallelEdges()).isFalse();

    addEdge(N1, N2, E12);
    IllegalArgumentException e =
        assertThrows(
            IllegalArgumentException.class,

    assertThat(e).hasMessageThat().contains(ERROR_REUSE_EDGE);
  }

  @Test
  public void addEdge_parallelEdge_notAllowed() {
    assume().that(graphIsMutable()).isTrue();
    assume().that(network.allowsParallelEdges()).isFalse();

    addEdge(N1, N2, E12);
    IllegalArgumentException e =
        assertThrows(
            IllegalArgumentException.class,

      NetworkBuilder<? super N, ? super E> builder,
      Map<N, NetworkConnections<N, E>> nodeConnections,
      Map<E, N> edgeToReferenceNode) {
    this.isDirected = builder.directed;
    this.allowsParallelEdges = builder.allowsParallelEdges;
    this.allowsSelfLoops = builder.allowsSelfLoops;
    this.nodeOrder = builder.nodeOrder.cast();
    this.edgeOrder = builder.edgeOrder.cast();

      NetworkBuilder<? super N, ? super E> builder,
      Map<N, NetworkConnections<N, E>> nodeConnections,
      Map<E, N> edgeToReferenceNode) {
    this.isDirected = builder.directed;
    this.allowsParallelEdges = builder.allowsParallelEdges;
    this.allowsSelfLoops = builder.allowsSelfLoops;
    this.nodeOrder = builder.nodeOrder.cast();
    this.edgeOrder = builder.edgeOrder.cast();

      GraphBuilder.directed().<String>immutable().addNode("B").build();

  private static final NetworkBuilder<?, ?> NETWORK_BUILDER_A =
      NetworkBuilder.directed().allowsParallelEdges(true).expectedNodeCount(10);
  private static final NetworkBuilder<?, ?> NETWORK_BUILDER_B =
      NetworkBuilder.directed().allowsSelfLoops(true).expectedNodeCount(16);

   * an edge connecting node A to node B if this {@link Network} has an edge connecting A to B.
   *
   * <p>If this network {@link #allowsParallelEdges() allows parallel edges}, parallel edges will be
   * treated as if collapsed into a single edge. For example, the {@link #degree(Object)} of a node

    return true;
  }

  private NetworkConnections<N, E> newConnections() {
    return isDirected()
        ? allowsParallelEdges()
            ? DirectedMultiNetworkConnections.<N, E>of()
            : DirectedNetworkConnections.<N, E>of()
        : allowsParallelEdges()
            ? UndirectedMultiNetworkConnections.<N, E>of()
            : UndirectedNetworkConnections.<N, E>of();
  }

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

    MutableNetwork<Integer, String> g2 =
        NetworkBuilder.from(network)
            .allowsParallelEdges(!network.allowsParallelEdges())
            .allowsSelfLoops(!network.allowsSelfLoops())
            .build();
    g2.addEdge(N1, N2, E12);

    assertThat(network).isEqualTo(g2);
  }

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

    MutableNetwork<Integer, String> g2 =
        NetworkBuilder.from(network)
            .allowsParallelEdges(!network.allowsParallelEdges())
            .allowsSelfLoops(!network.allowsSelfLoops())
            .build();
    g2.addEdge(N1, N2, E12);

    assertThat(network).isEqualTo(g2);
  }