private void addIllegalEdge(Point from, Point to, Class<? extends IntervalException> err) {
   try {
     Intervals.addHb(from, to);
     Assert.fail("No error");
   } catch (IntervalException e) {
     Assert.assertEquals("Wrong class", err, e.getClass());
   }
 }
 private void addLegalEdge(Point from, Point to) {
   Intervals.addHb(from, to);
 }