assertThat(toString).contains("valueB");
    assertThat(toString).contains("valueC");
    assertThat(toString).contains("valueD");
  }

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

  @Test