public static <N> EndpointPair<N> ordered(N source, N target) {
    return new Ordered<>(source, target);
  }

  /** Returns an {@link EndpointPair} representing the endpoints of an undirected edge. */
  public static <N> EndpointPair<N> unordered(N nodeU, N nodeV) {
    // Swap nodes on purpose to prevent callers from relying on the "ordering" of an unordered pair.
    return new Unordered<>(nodeV, nodeU);
  }

@NullUnmarked
public final class ElementOrderTest {
  // Node order tests

  @Test
  public void nodeOrder_none() {
    MutableGraph<Integer> graph = GraphBuilder.directed().nodeOrder(unordered()).build();

    assertThat(graph.nodeOrder()).isEqualTo(unordered());
  }

  @Test
  public void nodeOrder_insertion() {
    MutableGraph<Integer> graph = GraphBuilder.directed().nodeOrder(insertion()).build();

    addNodes(graph);

  boolean removeEdge(N nodeU, N nodeV);

  /**
   * Removes the edge connecting {@code endpoints}, if it is present.
   *
   * <p>If this graph is directed, {@code endpoints} must be ordered.
   *
   * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed
   * @return {@code true} if the graph was modified as a result of this call
   * @since 27.1
   */
  @CanIgnoreReturnValue

   *
   * <p>The default value is {@link ElementOrder#unordered() unordered} for mutable graphs. For
   * immutable graphs, this value is ignored; they always have a {@link ElementOrder#stable()
   * stable} order.
   *
   * @throws IllegalArgumentException if {@code incidentEdgeOrder} is not either {@code
   *     ElementOrder.unordered()} or {@code ElementOrder.stable()}.
   * @since 29.0
   */

  public static <S> ElementOrder<S> unordered() {
    return new ElementOrder<>(Type.UNORDERED, null);
  }

  /**
   * Returns an instance which specifies that ordering is guaranteed to be always be the same across
   * iterations, and across releases. Some methods may have stronger guarantees.
   *
   * <p>This instance is only useful in combination with {@code incidentEdgeOrder}, e.g. {@code

   *
   * <p>The default value is {@link ElementOrder#unordered() unordered} for mutable graphs. For
   * immutable graphs, this value is ignored; they always have a {@link ElementOrder#stable()
   * stable} order.
   *
   * @throws IllegalArgumentException if {@code incidentEdgeOrder} is not either {@code
   *     ElementOrder.unordered()} or {@code ElementOrder.stable()}.
   * @since 29.0
   */

 * 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
 *   <li>graphs whose edges have associated values
 * </ul>
 *
 * <p>{@code ValueGraph}, as a subtype of {@code Graph}, explicitly does not support parallel edges,

 *
 * <ul>
 *   <li>directed graphs
 *   <li>undirected graphs
 *   <li>graphs that do/don't allow parallel edges
 *   <li>graphs that do/don't allow self-loops
 *   <li>graphs whose nodes/edges are insertion-ordered, sorted, or unordered
 *   <li>graphs whose edges are <a
 *       href="https://github.com/google/guava/wiki/GraphsExplained#uniqueness">unique</a> objects
 * </ul>
 *
 * <h3>Building a {@code Network}</h3>
 *

   *     nodeV}, or null if there was no such edge.
   * @throws IllegalArgumentException if the introduction of the edge would violate {@link
   *     #allowsSelfLoops()}
   * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed
   * @since 27.1
   */
  @CanIgnoreReturnValue
  @Nullable V putEdgeValue(EndpointPair<N> endpoints, V value);

  /**

     * @return this {@code Builder} object
     * @throws IllegalArgumentException if the introduction of the edge would violate {@link
     *     #allowsSelfLoops()}
     * @throws IllegalArgumentException if the endpoints are unordered and the graph is directed
     */
    @CanIgnoreReturnValue
    public ImmutableValueGraph.Builder<N, V> putEdgeValue(EndpointPair<N> endpoints, V value) {
      mutableValueGraph.putEdgeValue(endpoints, value);