private void ApplyChangesAndTest(NotifyCollectionChangedEventArgs received, NotifyCollectionChangedAction Expected)
        {
            received.Should().NotBeNull();
            received.Action.Should().Be(Expected);

            int c = _Target.Count;
            
            Nullable<int> changes = _Target.ApplyChanges(received);
            changes.Should().HaveValue();
            _Target.Should().Equal(_Collection);
            changes.Should().Be(_Target.Count - c); 
        }