Don't try to purchase the same order twice

lms/djangoapps/shoppingcart/models.py

@@ -105,6 +105,8 @@ class Order(models.Model):
         `processor_reply_dump` - all the parameters returned by the processor
 
         """
+        if self.status == 'purchased':
+            return
         self.status = 'purchased'
         self.purchase_time = datetime.now(pytz.utc)
         self.bill_to_first = first

lms/djangoapps/shoppingcart/tests/test_models.py

@@ -103,6 +103,14 @@ class OrderTest(ModuleStoreTestCase):
                 # verify that e-mail wasn't sent
                 self.assertEquals(len(mail.outbox), 0)
 
+    def test_purchase_twice(self):
+        cart = Order.get_cart_for_user(self.user)
+        CertificateItem.add_to_order(cart, self.course_id, self.cost, 'honor')
+        # purchase the cart more than once
+        cart.purchase()
+        cart.purchase()
+        self.assertEquals(len(mail.outbox), 1)
+
     def purchase_with_data(self, cart):
         """ purchase a cart with billing information """
         CertificateItem.add_to_order(cart, self.course_id, self.cost, 'honor')
@@ -137,7 +145,6 @@ class OrderTest(ModuleStoreTestCase):
     @patch.dict(settings.MITX_FEATURES, {'STORE_BILLING_INFO': False})
     def test_billing_info_storage_off(self):
         cart = Order.get_cart_for_user(self.user)
-        cart = Order.get_cart_for_user(self.user)
         self.purchase_with_data(cart)
         self.assertNotEqual(cart.bill_to_first, '')
         self.assertNotEqual(cart.bill_to_last, '')