private void _testFanoutWithPeek(boolean after) throws Exception {
    Topology t = newTopology();
    Graph g = t.graph();

    /*                            -- Filter -- Sink(.)
     *                           /
     * Source -- Peek -- FanOut ---- Modify -- Sink(@)
     *
     */
    TStream<Integer> d = integers(t, 1, 2, 3);
    List<Integer> peekedValues = new ArrayList<>();

    if (!after) d.peek(tuple -> peekedValues.add(tuple));

    TStream<Integer> df = d.filter(tuple -> tuple.intValue() > 0);
    TStream<Integer> dm = d.modify(tuple -> new Integer(tuple.intValue() + 1));

    if (after) d.peek(tuple -> peekedValues.add(tuple));

    df.sink(tuple -> System.out.print("."));
    dm.sink(tuple -> System.out.print("@"));

    assertEquals(7, g.getVertices().size());
    assertEquals(6, g.getEdges().size());

    // Insert counter metrics into all the streams
    Metrics.counter(t);

    printGraph(g);

    assertEquals(10, g.getVertices().size());
    assertEquals(9, g.getEdges().size());
  }