NonComparableSuperClass node5 = new NonComparableSuperClass(5);
    NonComparableSuperClass node7 = new NonComparableSuperClass(7);

    graph.addNode(node1);
    graph.addNode(node7);
    graph.addNode(node5);
    graph.addNode(node3);

    assertThat(graph.nodeOrder().comparator()).isEqualTo(comparator);
    assertThat(graph.nodes()).containsExactly(node1, node3, node5, node7).inOrder();
  }

  @Test