anchor.diff:  
       deliverChanges();
   
  -    expect(manager.selectedIndex, -1);
  -    expect(manager.selectedValue, null);
  -    expect(manager.hasSelection, isFalse);
  +    _expectNoSelection(manager);
   
       _expectPropChanges(changes, ['hasSelection', 'selectedIndex',
                                    'selectedItem']);
  
positive.code: 
      expect(manager.selectedIndex, 2);
      expect(manager.selectedValue, 3);
      expect(manager.hasSelection, isTrue);
  
      _expectPropChanges(changes, []);
  
  
negative.code: 
      expect(manager.selectedIndex, 4);
      expect(manager.selectedValue, 5);
      _expectSelection(manager);
  
      _expectPropChanges(changes, ['selectedIndex', 'selectedItem']);
  
  