diff --git a/uncloud_pay/models.py b/uncloud_pay/models.py
index 0898c60..1f75dd7 100644
--- a/uncloud_pay/models.py
+++ b/uncloud_pay/models.py
@@ -628,12 +628,13 @@ class Order(models.Model):
 
         super().save(*args, **kwargs)
 
-#        Bill.generate_for(self.starting_date.year, self.starting_date.month, self.owner)
+    def generate_initial_bill(self):
+        return Bill.generate_for(self.starting_date.year, self.starting_date.month, self.owner)
 
-    # # Used by uncloud_pay tests.
-    # @property
-    # def bills(self):
-    #     return Bill.objects.filter(order=self)
+    # Used by uncloud_pay tests.
+    @property
+    def bills(self):
+        return Bill.objects.filter(order=self)
 
     def __str__(self):
         return "Order {} created at {}, {}->{}, recurring period {}. One time price {}, recurring price {}".format(
diff --git a/uncloud_pay/tests.py b/uncloud_pay/tests.py
index 64f0442..00ee294 100644
--- a/uncloud_pay/tests.py
+++ b/uncloud_pay/tests.py
@@ -31,11 +31,13 @@ class BillingTestCase(TestCase):
                 starting_date=starting_date,
                 ending_date=ending_date,
                 recurring_period=RecurringPeriod.PER_MONTH,
+                recurring_price=recurring_price,
+                one_time_price=one_time_price,
+                description=description,
                 billing_address=self.billing_address)
-        order.add_record(one_time_price, recurring_price, description)
 
         # Generate & check bill for first month: full recurring_price + setup.
-        first_month_bills = order.bills # Initial bill generated at order creation.
+        first_month_bills = order.generate_initial_bill()
         self.assertEqual(len(first_month_bills), 1)
         self.assertEqual(first_month_bills[0].amount, one_time_price + recurring_price)
 
@@ -49,7 +51,7 @@ class BillingTestCase(TestCase):
         self.assertEqual(len(third_month_bills), 1)
         # 31 days in May.
         self.assertEqual(float(third_month_bills[0].amount),
-                round((7/31) * recurring_price, AMOUNT_DECIMALS))
+                round(round((7/31), AMOUNT_DECIMALS) * recurring_price, AMOUNT_DECIMALS))
 
         # Check that running Bill.generate_for() twice does not create duplicates.
         self.assertEqual(len(Bill.generate_for(2020, 3, self.user)), 0)
@@ -66,11 +68,13 @@ class BillingTestCase(TestCase):
                 owner=self.user,
                 starting_date=starting_date,
                 recurring_period=RecurringPeriod.PER_YEAR,
+                recurring_price=recurring_price,
+                one_time_price=one_time_price,
+                description=description,
                 billing_address=self.billing_address)
-        order.add_record(one_time_price, recurring_price, description)
 
         # Generate & check bill for first year: recurring_price + setup.
-        first_year_bills = order.bills # Initial bill generated at order creation.
+        first_year_bills = order.generate_initial_bill()
         self.assertEqual(len(first_year_bills), 1)
         self.assertEqual(first_year_bills[0].starting_date.date(),
                 date.fromisoformat('2020-03-31'))
@@ -108,11 +112,13 @@ class BillingTestCase(TestCase):
                 starting_date=starting_date,
                 ending_date=ending_date,
                 recurring_period=RecurringPeriod.PER_HOUR,
+                recurring_price=recurring_price,
+                one_time_price=one_time_price,
+                description=description,
                 billing_address=self.billing_address)
-        order.add_record(one_time_price, recurring_price, description)
 
         # Generate & check bill for first month: recurring_price + setup.
-        first_month_bills = order.bills
+        first_month_bills = order.generate_initial_bill()
         self.assertEqual(len(first_month_bills), 1)
         self.assertEqual(float(first_month_bills[0].amount),
                 round(16 * recurring_price, AMOUNT_DECIMALS) + one_time_price)
@@ -137,28 +143,32 @@ class ProductActivationTestCase(TestCase):
 
     def test_product_activation(self):
         starting_date = datetime.fromisoformat('2020-03-01')
+        one_time_price = 0
+        recurring_price = 1
+        description = "Test Product"
 
         order = Order.objects.create(
                 owner=self.user,
                 starting_date=starting_date,
                 recurring_period=RecurringPeriod.PER_MONTH,
+                recurring_price=recurring_price,
+                one_time_price=one_time_price,
+                description=description,
                 billing_address=self.billing_address)
 
         product = GenericServiceProduct(
-                custom_description="Test product",
-                custom_one_time_price=0,
-                custom_recurring_price=20,
+                custom_description=description,
+                custom_one_time_price=one_time_price,
+                custom_recurring_price=recurring_price,
                 owner=self.user,
                 order=order)
         product.save()
 
-        # XXX: to be automated.
-        order.add_record(product.one_time_price, product.recurring_price, product.description)
-
         # Validate initial state: must be awaiting payment.
         self.assertEqual(product.status, UncloudStatus.AWAITING_PAYMENT)
 
         # Pay initial bill, check that product is activated.
+        order.generate_initial_bill()
         amount = product.order.bills[0].amount
         payment = Payment(owner=self.user, amount=amount)
         payment.save()