* @throws IllegalArgumentException if the introduction of the edge would violate {@link
   *     #allowsParallelEdges()} or {@link #allowsSelfLoops()}
   * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed
   * @since 27.1
   */
  @CanIgnoreReturnValue
  boolean addEdge(EndpointPair<N> endpoints, E edge);

  /**

     * endpoints}) if one is not already present.
     *
     * <p>If this graph is directed, {@code endpoints} must be ordered and the added edge will be
     * directed; if it is undirected, the added edge will be undirected.
     *
     * <p>If this graph is directed, {@code endpoints} must be ordered.
     *
     * <p>If either or both endpoints are not already present in this graph, this method will

   * edges().contains(endpoints)}.
   *
   * <p>Unlike the other {@code EndpointPair}-accepting methods, this method does not throw if the
   * endpoints are unordered; it simply returns false. This is for consistency with the behavior of
   * {@link Collection#contains(Object)} (which does not generally throw if the object cannot be

 * terms</a>):
 *
 * <ul>
 *   <li>directed graphs
 *   <li>undirected graphs
 *   <li>graphs that do/don't allow self-loops
 *   <li>graphs whose nodes/edges are insertion-ordered, sorted, or unordered
 * </ul>
 *
 * <p>{@code Graph} explicitly does not support parallel edges, and forbids implementations or
 * extensions with parallel edges. If you need parallel edges, use {@link Network}.
 *

     * @throws IllegalArgumentException if the introduction of the edge would violate {@link
     *     #allowsParallelEdges()} or {@link #allowsSelfLoops()}
     * @throws IllegalArgumentException if the endpoints are unordered and the network is directed
     */
    @CanIgnoreReturnValue
    public ImmutableNetwork.Builder<N, E> addEdge(EndpointPair<N> endpoints, E edge) {
      mutableNetwork.addEdge(endpoints, edge);
      return this;

              Iterators.transform(
                  predecessors().iterator(),
                  (N predecessor) -> EndpointPair.ordered(predecessor, thisNode)),
              Iterators.transform(
                  successors().iterator(),
                  (N successor) -> EndpointPair.ordered(thisNode, successor)));
    } else {
      resultWithDoubleSelfLoop =
          Iterators.transform(

    populateTShapedGraph();

    assertThat(graph.edges())
        .containsExactly(
            EndpointPair.unordered(1, 2),
            EndpointPair.unordered(1, 4),
            EndpointPair.unordered(1, 3),
            EndpointPair.unordered(4, 5))
        .inOrder();
  }

  @Test
  public void stableIncidentEdgeOrder_adjacentNodes_returnsInConnectingEdgeInsertionOrder() {

    populateTShapedGraph();

    assertThat(graph.edges())
        .containsExactly(
            EndpointPair.unordered(1, 2),
            EndpointPair.unordered(1, 4),
            EndpointPair.unordered(1, 3),
            EndpointPair.unordered(4, 5))
        .inOrder();
  }

  @Test
  public void stableIncidentEdgeOrder_adjacentNodes_returnsInConnectingEdgeInsertionOrder() {

                        (N predecessor) ->
                            graph.isDirected()
                                ? EndpointPair.ordered(predecessor, node)
                                : EndpointPair.unordered(predecessor, node)));
              }
            };
        return nodeInvalidatableSet(incident, node);
      }

      @Override

    assertThat(graph.hasEdgeConnecting(EndpointPair.unordered(1, 2))).isFalse();
    assertThat(graph.hasEdgeConnecting(EndpointPair.unordered(2, 1))).isFalse();
  }

  @Test
  public void hasEdgeConnecting_undirected_correct() {
    graph = ValueGraphBuilder.undirected().build();
    graph.putEdgeValue(1, 2, "A");
    assertThat(graph.hasEdgeConnecting(EndpointPair.unordered(1, 2))).isTrue();
  }

  @Test