* @throws IllegalArgumentException if {@code incidentEdgeOrder} is not either {@code
   *     ElementOrder.unordered()} or {@code ElementOrder.stable()}.
   * @since 29.0
   */
  public <N1 extends N> ValueGraphBuilder<N1, V> incidentEdgeOrder(
      ElementOrder<N1> incidentEdgeOrder) {
    checkArgument(
        incidentEdgeOrder.type() == ElementOrder.Type.UNORDERED
            || incidentEdgeOrder.type() == ElementOrder.Type.STABLE,

    assume().that(graph.incidentEdgeOrder().type()).isEqualTo(ElementOrder.Type.STABLE);

    populateTShapedGraph();

    assertThat(graph.adjacentNodes(1)).containsExactly(2, 4, 3).inOrder();
  }

  @Test
  public void stableIncidentEdgeOrder_predecessors_returnsInConnectingEdgeInsertionOrder() {
    assume().that(graph.incidentEdgeOrder().type()).isEqualTo(ElementOrder.Type.STABLE);

    assume().that(graph.incidentEdgeOrder().type()).isEqualTo(ElementOrder.Type.STABLE);

    populateTShapedGraph();

    assertThat(graph.adjacentNodes(1)).containsExactly(2, 4, 3).inOrder();
  }

  @Test
  public void stableIncidentEdgeOrder_predecessors_returnsInConnectingEdgeInsertionOrder() {
    assume().that(graph.incidentEdgeOrder().type()).isEqualTo(ElementOrder.Type.STABLE);

  }

  static <N, V> DirectedGraphConnections<N, V> of(ElementOrder<N> incidentEdgeOrder) {
    // We store predecessors and successors in the same map, so double the initial capacity.
    int initialCapacity = INNER_CAPACITY * 2;

    List<NodeConnection<N>> orderedNodeConnections;
    switch (incidentEdgeOrder.type()) {
      case UNORDERED:
        orderedNodeConnections = null;
        break;

    graph = ValueGraphBuilder.directed().incidentEdgeOrder(ElementOrder.unordered()).build();
    assertThat(graph.incidentEdgeOrder()).isEqualTo(ElementOrder.unordered());
  }

  @Test
  public void incidentEdgeOrder_stable() {
    graph = ValueGraphBuilder.directed().incidentEdgeOrder(ElementOrder.stable()).build();
    assertThat(graph.incidentEdgeOrder()).isEqualTo(ElementOrder.stable());
  }

  @Test

   *
   * <p>This instance is only useful in combination with {@code incidentEdgeOrder}, e.g. {@code
   * graphBuilder.incidentEdgeOrder(ElementOrder.stable())}.
   *
   * <h3>In combination with {@code incidentEdgeOrder}</h3>
   *
   * <p>{@code incidentEdgeOrder(ElementOrder.stable())} guarantees the ordering of the returned
   * collections of the following methods:
   *
   * <ul>

   *
   * <p>This instance is only useful in combination with {@code incidentEdgeOrder}, e.g. {@code
   * graphBuilder.incidentEdgeOrder(ElementOrder.stable())}.
   *
   * <h3>In combination with {@code incidentEdgeOrder}</h3>
   *
   * <p>{@code incidentEdgeOrder(ElementOrder.stable())} guarantees the ordering of the returned
   * collections of the following methods:
   *
   * <ul>

    graph = ValueGraphBuilder.directed().incidentEdgeOrder(ElementOrder.unordered()).build();
    assertThat(graph.incidentEdgeOrder()).isEqualTo(ElementOrder.unordered());
  }

  @Test
  public void incidentEdgeOrder_stable() {
    graph = ValueGraphBuilder.directed().incidentEdgeOrder(ElementOrder.stable()).build();
    assertThat(graph.incidentEdgeOrder()).isEqualTo(ElementOrder.stable());
  }

  @Test

    private final MutableGraph<N> mutableGraph;

    Builder(GraphBuilder<N> graphBuilder) {
      // The incidentEdgeOrder for immutable graphs is always stable. However, we don't want to
      // modify this builder, so we make a copy instead.
      this.mutableGraph = graphBuilder.copy().incidentEdgeOrder(ElementOrder.<N>stable()).build();
    }

    /**
     * Adds {@code node} if it is not already present.
     *

      }

      @Override
      public ElementOrder<N> nodeOrder() {
        return AbstractValueGraph.this.nodeOrder();
      }

      @Override
      public ElementOrder<N> incidentEdgeOrder() {
        return AbstractValueGraph.this.incidentEdgeOrder();
      }

      @Override
      public Set<N> adjacentNodes(N node) {
        return AbstractValueGraph.this.adjacentNodes(node);
      }

      @Override