ShoppingCart.Unclear.cs

public class ShoppingCart
{
    public IList<CartItem> Items { get; set; }
    public decimal CartTotal { get; set; }

    public void Add(CartItem item)
    {
        if (Items.Any(x => x.StockKeepingUnit == item.StockKeepingUnit))
        {
            var i = Items.First(x => x.StockKeepingUnit == item.StockKeepingUnit);
            item.Qty += i.Qty;
        }
        else
        {
            Items.Add(item);
        } 
        
        // Extra tracking we need to do for customer service and extra debug tracing
        Track();
    }

    private void Track()
    {
        var t = Items.Sum(x => x.TotaPrice);
        CartTotal = t;
        CustomerTrackingService.TrackTotalInShoppingCart(t);
    }
}