Restrict the basket to one voucher

ecommerce/extensions/basket/tests/test_utils.py

@@ -2,7 +2,7 @@ import ddt
 
 from django.test import RequestFactory
 from oscar.core.loading import get_model
-from oscar.test.factories import ProductFactory, RangeFactory
+from oscar.test.factories import ProductFactory, RangeFactory, VoucherFactory
 
 from ecommerce.extensions.basket.utils import get_certificate_type_display_value, prepare_basket
 from ecommerce.extensions.partner.models import StockRecord
@@ -45,6 +45,20 @@ class BasketUtilsTests(TestCase):
         self.assertEqual(basket.total_discount, 10.00)
         self.assertEqual(basket.total_excl_tax, 90.00)
 
+    def test_multiple_vouchers(self):
+        """ Verify only the last entered voucher is contained in the basket. """
+        product = ProductFactory()
+        voucher1 = VoucherFactory(code='FIRST')
+        basket = prepare_basket(self.request, product, voucher1)
+        self.assertEqual(basket.vouchers.count(), 1)
+        self.assertEqual(basket.vouchers.first(), voucher1)
+
+        voucher2 = VoucherFactory(code='SECOND')
+        new_basket = prepare_basket(self.request, product, voucher2)
+        self.assertEqual(basket, new_basket)
+        self.assertEqual(new_basket.vouchers.count(), 1)
+        self.assertEqual(new_basket.vouchers.first(), voucher2)
+
     def test_prepare_basket_without_voucher(self):
         """ Verify a basket is returned and does not contain a voucher. """
         product = ProductFactory()

ecommerce/extensions/basket/utils.py

@@ -13,7 +13,9 @@ def prepare_basket(request, product, voucher=None):
     Create or get the basket, add the product, and apply a voucher.
 
     Existing baskets are merged. The specified product will
-    be added to the remaining open basket. The Voucher is applied to the basket.
+    be added to the remaining open basket. If a voucher is passed, all existing
+    ones added to the basket are removed because we allow only one voucher per
+    basket after the Voucher is applied to the basket.
 
     Arguments:
         request (Request): The request object made to the view.
@@ -27,6 +29,8 @@ def prepare_basket(request, product, voucher=None):
     basket.flush()
     basket.add_product(product, 1)
     if voucher:
+        for v in basket.vouchers.all():
+            basket.vouchers.remove(v)
         basket.vouchers.add(voucher)
         Applicator().apply(basket, request.user, request)
         logger.info('Applied Voucher [%s] to basket [%s].', voucher.code, basket.id)