Shopping cart

I have six feature files for this exercise:
1. add_quantity.feature: Add Products to Shopping Cart
2. change_quantity.feature: Change Quantity of Products in Shopping Cart
3. remove_quantity.feature: Remove Products from Shopping Cart
4. coupon.feature: Add Coupons to Shopping Cart
5. navigate_to_item_pages.feature: Navigate from Shopping Cart to Item Page
6. shipping_estimate.feature:  Obtain shipping estimates
what if a customer tries to enter a non-numerical value into the product quantity box?