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