@Test
  public void testHighLevelAccess() {
    Link link = nw.getLinkById(3L);

    Double val = 1.23;

    dp.setVehiclesPerMeterOnLink(link, val);

    assertEquals((Double) 1.23, dp.getVehiclesPerMeterOnLink(link));
  }
  @Test
  public void testPrimitiveAccess() {
    Map<String, Double> vpm = new HashMap<String, Double>();

    dp.setVehiclesPerMeter(vpm);

    Double val = 1.23;
    vpm.put("3", val);

    assertEquals((Double) 1.23, dp.getVehiclesPerMeter().get("3"));
  }