final boolean graphIsMutable() {
    return graphAsMutableGraph != null;
  }

  @Before
  public final void init() {
    graph = createGraph();
    if (graph instanceof MutableGraph) {
      graphAsMutableGraph = (MutableGraph<Integer>) graph;
    }
  }

  @After
  public final void validateGraphState() {
    validateGraph(graph);
  }

  static <N> void validateGraph(Graph<N> graph) {

  final boolean graphIsMutable() {
    return graphAsMutableGraph != null;
  }

  @Before
  public final void init() {
    graph = createGraph();
    if (graph instanceof MutableGraph) {
      graphAsMutableGraph = (MutableGraph<Integer>) graph;
    }
  }

  @After
  public final void validateGraphState() {
    validateGraph(graph);
  }

  static <N> void validateGraph(Graph<N> graph) {