}

  static void assertStronglyEquivalent(Network<?, ?> networkA, Network<?, ?> networkB) {
    // Properties not covered by equals()
    assertThat(networkA.allowsParallelEdges()).isEqualTo(networkB.allowsParallelEdges());
    assertThat(networkA.allowsSelfLoops()).isEqualTo(networkB.allowsSelfLoops());
    assertThat(networkA.nodeOrder()).isEqualTo(networkB.nodeOrder());

   * 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

      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();

    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,

          + "edgesConnecting() instead.";
  static final String PARALLEL_EDGES_NOT_ALLOWED =
      "Nodes %s and %s are already connected by a different edge. To construct a graph "
          + "that allows parallel edges, call allowsParallelEdges(true) on the Builder.";
  static final String SELF_LOOPS_NOT_ALLOWED =
      "Cannot add self-loop edge on node %s, as self-loops are not allowed. To construct a graph "

          + "edgesConnecting() instead.";
  static final String PARALLEL_EDGES_NOT_ALLOWED =
      "Nodes %s and %s are already connected by a different edge. To construct a graph "
          + "that allows parallel edges, call allowsParallelEdges(true) on the Builder.";
  static final String SELF_LOOPS_NOT_ALLOWED =
      "Cannot add self-loop edge on node %s, as self-loops are not allowed. To construct a graph "

  }

  /** Returns a string representation of this network. */
  @Override
  public String toString() {
    return "isDirected: "
        + isDirected()
        + ", allowsParallelEdges: "
        + allowsParallelEdges()
        + ", allowsSelfLoops: "
        + allowsSelfLoops()
        + ", nodes: "
        + nodes()
        + ", edges: "
        + edgeIncidentNodesMap(this);
  }

  /**

  }

  /** Returns a string representation of this network. */
  @Override
  public String toString() {
    return "isDirected: "
        + isDirected()
        + ", allowsParallelEdges: "
        + allowsParallelEdges()
        + ", allowsSelfLoops: "
        + allowsSelfLoops()
        + ", nodes: "
        + nodes()
        + ", edges: "
        + edgeIncidentNodesMap(this);
  }

  /**

   * 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