@Test
public void testRetrieveNonOccurrence() {

    QuickstartCqlVisitor v = visitLogic(
            "valueset \"Office Visit\" = ValueSet('2.16.840.1.113883.3.464.1003.101.12.1001')\n" +
            "let encounter = [NonOccurrence of Encounter, Performance: \"Office Visit\"]");
    Collection<Retrieve> rSet = v.getRetrieves();
    assertEquals(rSet.size(), 1);
    Retrieve r = rSet.iterator().next();
    assertEquals(r.getExistence(), Retrieve.Existence.NonOccurrence);
    assertEquals(r.getTopic(), "Encounter");
    assertEquals(r.getModality(), "Performance");
    assertEquals(r.getValueset(), new ValueSet("2.16.840.1.113883.3.464.1003.101.12.1001"));
}