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);
  }

        .containsExactly("chicken", "egg");
    assertThat(unordered.adjacentNode(unordered.nodeU())).isEqualTo(unordered.nodeV());
    assertThat(unordered.adjacentNode(unordered.nodeV())).isEqualTo(unordered.nodeU());
    assertThat(unordered.toString()).contains("chicken");
    assertThat(unordered.toString()).contains("egg");
  }

  @Test
  public void testSelfLoop() {

        .containsExactly("chicken", "egg");
    assertThat(unordered.adjacentNode(unordered.nodeU())).isEqualTo(unordered.nodeV());
    assertThat(unordered.adjacentNode(unordered.nodeV())).isEqualTo(unordered.nodeU());
    assertThat(unordered.toString()).contains("chicken");
    assertThat(unordered.toString()).contains("egg");
  }

  @Test
  public void testSelfLoop() {

@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
   */

   *
   * <p>Note: This default implementation is overkill (but valid) for an unordered container. An
   * equally valid implementation for an unordered container is to throw an exception. The chosen
   * implementation, however, has the advantage of working for insertion-ordered containers, as
   * well.
   */
  @Override
  public List<Integer> order(List<Integer> insertionOrder) {

  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>Note: This default implementation is overkill (but valid) for an unordered container. An
   * equally valid implementation for an unordered container is to throw an exception. The chosen
   * implementation, however, has the advantage of working for insertion-ordered containers, as
   * well.
   */
  @Override
  public List<String> order(List<String> insertionOrder) {

   *
   * <p>Note: This default implementation is overkill (but valid) for an unordered container. An
   * equally valid implementation for an unordered container is to throw an exception. The chosen
   * implementation, however, has the advantage of working for insertion-ordered containers, as
   * well.
   */
  @Override
  public List<Integer> order(List<Integer> insertionOrder) {