/**
   * Computes the function of current and new value. Subclasses should open-code this update
   * function for most uses, but the virtualized form is needed within retryUpdate.
   *
   * @param currentValue the current value (of either base or a cell)
   * @param newValue the argument from a user update call
   * @return result of the update function
   */
  abstract long fn(long currentValue, long newValue);

  /**

  /**
   * Computes the function of current and new value. Subclasses should open-code this update
   * function for most uses, but the virtualized form is needed within retryUpdate.
   *
   * @param currentValue the current value (of either base or a cell)
   * @param newValue the argument from a user update call
   * @return result of the update function
   */
  abstract long fn(long currentValue, long newValue);

  /**

      assertThat(directedGraph.outDegree(node)).isSameInstanceAs(transpose.inDegree(node));
    }

    assertThat(transpose.successors(N1)).doesNotContain(N2);
    directedGraph.putEdge(N2, N1);
    // View should be updated.
    assertThat(transpose.successors(N1)).contains(N2);
    AbstractGraphTest.validateGraph(transpose);
  }

  @Test
  public void transpose_undirectedValueGraph() {

   * configured with. The initial value of this is the same as the {@code permitsPerSecond} argument
   * passed in the factory method that produced this {@code RateLimiter}, and it is only updated
   * after invocations to {@linkplain #setRate}.
   */
  public final double getRate() {
    synchronized (mutex()) {
      return doGetRate();
    }
  }

  abstract double doGetRate();

  /**
   * Computes the function of current and new value. Subclasses should open-code this update
   * function for most uses, but the virtualized form is needed within retryUpdate.
   *
   * @param currentValue the current value (of either base or a cell)
   * @param newValue the argument from a user update call
   * @return result of the update function
   */
  abstract long fn(long currentValue, long newValue);

  /**

  }

  // Stable order tests

  // Note: Stable order means that the ordering doesn't change between iterations and versions.
  // Ideally, the ordering in test should never be updated.
  @Test
  public void stableIncidentEdgeOrder_edges_returnsInStableOrder() {
    assume().that(graph.incidentEdgeOrder().type()).isEqualTo(ElementOrder.Type.STABLE);

    populateTShapedGraph();

  }

  // Stable order tests

  // Note: Stable order means that the ordering doesn't change between iterations and versions.
  // Ideally, the ordering in test should never be updated.
  @Test
  public void stableIncidentEdgeOrder_edges_returnsInStableOrder() {
    assume().that(graph.incidentEdgeOrder().type()).isEqualTo(ElementOrder.Type.STABLE);

    populateStarShapedGraph();

  }

  // Stable order tests

  // Note: Stable order means that the ordering doesn't change between iterations and versions.
  // Ideally, the ordering in test should never be updated.
  @Test
  public void stableIncidentEdgeOrder_edges_returnsInStableOrder() {
    assume().that(graph.incidentEdgeOrder().type()).isEqualTo(ElementOrder.Type.STABLE);

    populateStarShapedGraph();

    // we really just want to wait for the thread to be in the failure callback so we wait for that
    // explicitly instead.
    failEnter.await();
    assertFalse("State should be updated before calling listeners", manager.isHealthy());
    // now we want to stop the services.
    Thread stoppingThread =
        new Thread() {
          @Override
          public void run() {

  }

  // Stable order tests

  // Note: Stable order means that the ordering doesn't change between iterations and versions.
  // Ideally, the ordering in test should never be updated.
  @Test
  public void stableIncidentEdgeOrder_edges_returnsInStableOrder() {
    assume().that(graph.incidentEdgeOrder().type()).isEqualTo(ElementOrder.Type.STABLE);

    populateTShapedGraph();