    >>> from zope.annotation.interfaces import IAnnotations
    >>> from decimal import Decimal
    >>> from collective.cart.core.interfaces import (
    ...     ICartProduct,
    ...     IPortal,
    ...     IProduct,
    ... )
    >>> from collective.cart.shipping.interfaces import ICart
    >>> doc00 = portal.doc00
    >>> product00 = IProduct(doc00)
    >>> product00.stock
    0
    >>> uid = doc00.UID()
    >>> quantity = '2'
    >>> form = dict(uid=uid, quantity=quantity)
    >>> IPortal(doc00).add_to_cart(form)
    >>> cart = IPortal(doc00).cart
    >>> cart
    <Cart at /plone/cfolder/1>
    >>> ICart(cart).weight
    0
    >>> cart.totals ==  {'products_cost': Decimal('200.00'), 'shipping_cost': Decimal('10.00')}
    True
    >>> cart.total_cost == Decimal('210.00')
    True

