public void check(String gt, String ad, String aq, Double expQad) {
   final VcfRecord rec = new VcfRecord("seq", 0, "A");
   rec.addFormatAndSample("GT", gt);
   rec.addFormatAndSample("AD", ad);
   rec.addFormatAndSample("AQ", aq);
   assertEquals(expQad, new MeanQualityDifferenceAnnotation().getValue(rec, 0));
 }