@Test
public void orderTopDown() {

    final HashMap<InterpolationVariable, Integer> map = new HashMap<>();
    map.put(new InterpolationVariable("var",
                                      DataType.TYPE_DATE,
                                      "Person",
                                      "birthday"), 0);
    map.put(new InterpolationVariable("var",
                                      DataType.TYPE_DATE,
                                      "Person",
                                      "dateOfDeath"), 1);
    map.put(new InterpolationVariable("p",
                                      DataType.TYPE_DATE,
                                      "Person",
                                      "dateOfDeath"), 2);
    final Map<InterpolationVariable, Integer> result = new InterpolationVariableCollector(map).getMap();
    assertEquals(2, result.size());
    final Iterator<Integer> iterator = result.values().iterator();
    assertEquals(1, (int) iterator.next());
    assertEquals(0, (int) iterator.next());
}