[Tests] Verify basket total amount after rounding

tests/integration/basket/test_total.py

@@ -0,0 +1,69 @@
+from decimal import Decimal as D
+
+from django.test import TestCase
+from django.test.utils import override_settings
+
+from oscar.apps.basket.models import Basket
+from oscar.apps.offer import models
+from oscar.apps.partner import strategy
+from oscar.test.basket import add_product
+
+
+def create_fixed_tax_basket(price):
+    basket = Basket.objects.create()
+    basket.strategy = strategy.UK()
+    add_product(basket, D(price), 1)
+    return basket
+
+
+class TestBasketTotalAfterRounding(TestCase):
+    def setUp(self):
+        product_range = models.Range.objects.create(
+            name="All products", includes_all_products=True
+        )
+        condition = models.CountCondition.objects.create(
+            range=product_range, type=models.Condition.COUNT, value=1
+        )
+        self.benefit = models.Benefit.objects.create(
+            range=product_range,
+            type=models.Benefit.FIXED,
+            value=D("11.45"),
+        )
+        self.offer = models.ConditionalOffer(
+            name="Test",
+            offer_type=models.ConditionalOffer.SITE,
+            condition=condition,
+            benefit=self.benefit,
+        )
+
+    @override_settings(OSCAR_OFFERS_INCL_TAX=True)
+    def test_total_excl_tax_precision_down(self):
+        basket = create_fixed_tax_basket(9.99)
+        self.benefit.value = D("4.13")
+        self.offer.apply_benefit(basket)
+
+        # 9.99-round(3.441) => 9.99-3.44 = 6.55
+        self.assertEqual(basket.total_excl_tax, D("6.55"))
+
+    @override_settings(OSCAR_OFFERS_INCL_TAX=True)
+    def test_total_excl_tax_precision_up(self):
+        basket = create_fixed_tax_basket(9.99)
+        self.benefit.value = D("4.14")
+        self.offer.apply_benefit(basket)
+
+        # 9.99-round(3.449) => 9.99-3.45 = 6.54
+        self.assertEqual(basket.total_excl_tax, D("6.54"))
+
+    def test_total_incl_tax_precision_down(self):
+        basket = create_fixed_tax_basket(20.37)
+        self.offer.apply_benefit(basket)
+
+        # 10.704 rounded to 10.70
+        self.assertEqual(basket.total_incl_tax, D("10.70"))
+
+    def test_total_incl_tax_precision_up(self):
+        basket = create_fixed_tax_basket(20.38)
+        self.offer.apply_benefit(basket)
+
+        # 10.716 rounded to 10.72
+        self.assertEqual(basket.total_incl_tax, D("10.72"))