public void InsertTest()
        {
            _target.Add("1");
            _target.Add("2");
            _target.Insert(1, "xxx");

            _target.Is("1", "xxx", "2");
            _collectionChanged.SelectMany(x => x.NewItems.Cast <string>())
            .Is("1", "2", "xxx");
            _collectionChanged.Select(x => x.Action)
            .Is(NotifyCollectionChangedAction.Add, NotifyCollectionChangedAction.Add, NotifyCollectionChangedAction.Add);
        }