Expand groupr regression test to verify invoice coupon display

Extended the free coupon checkout test to also verify that:
- Checkout completion creates an invoice with coupon redemptions
- Invoice page displays discount breakdown with coupon information
- Coupon codes and descriptions appear on invoice
- Discount amounts are calculated correctly

This ensures the invoice discount display enhancement works end-to-end.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

make_post_sell/tests/test_functional.py

@@ -713,25 +713,63 @@ class AuthenticatedFunctionalTests(FunctionalTests):
         
         # 6. SUCCESS! We reached the checkout page without AttributeError crash
         # This validates that the original bug (stripe_user_shop.active_card AttributeError) is fixed
-        # The bug occurred when stripe_user_shop was None for free carts, causing:
-        # AttributeError: 'NoneType' object has no attribute 'active_card'
-        # 
-        # By reaching this point, we've proven the code properly handles stripe_user_shop=None
-        
-        # NOTE: We intentionally stop here rather than completing the full checkout because:
-        # 1. The core AttributeError bug fix has been validated
-        # 2. Complete checkout has transaction management issues in the test environment
-        # 3. groupr's actual error was hitting the checkout page, not completing the transaction
         
         print("✓ REGRESSION TEST PASSED: Free coupon checkout reaches confirmation without AttributeError")
         print("✓ Core bug fix validated: stripe_user_shop=None properly handled in cart.py:712")
         
-        # 7. Complete the download flow after free coupon checkout
-        # Simulate successful purchase by creating user-product relationship
+        # 7. Complete the actual checkout to create a real invoice
+        # Now that transaction management is fixed, we can safely complete checkout
+        complete_checkout_res = self.testapp.post(
+            f"/u/cart/{user_cart.id}/complete/checkout",
+            {
+                "csrf_token": self.get_csrf_token(shop.uuid_str),
+            },
+        )
+        
+        # Should redirect after successful completion
+        self.assertEqual(complete_checkout_res.status_int, 302)
+        print(f"✓ CHECKOUT COMPLETED: Redirected to {complete_checkout_res.location}")
+        
+        # Transaction should have committed successfully
+        
+        # 8. Find and verify the invoice shows coupon information
+        # Get the created invoice from the database
+        from ..models.invoice import Invoice
+        invoice = self.dbsession.query(Invoice).first()
+        self.assertIsNotNone(invoice, "Invoice should be created after checkout completion")
+        
+        # Verify invoice has the coupon redemption
+        coupon_redemptions = list(invoice.coupon_redemptions)
+        self.assertEqual(len(coupon_redemptions), 1, "Invoice should have one coupon redemption")
+        self.assertEqual(coupon_redemptions[0].coupon.code, self.coupon2_params["code"])
+        
+        # 9. Test the invoice page displays coupon information
+        invoice_res = self.testapp.get(f"/i/{invoice.id}")
+        self.assertEqual(invoice_res.status_int, 200)
+        invoice_body = invoice_res.body.decode()
+        
+        # Verify coupon information appears on invoice
+        self.assertIn("Discounts Applied", invoice_body)
+        self.assertIn(self.coupon2_params["code"], invoice_body)  # Coupon code
+        self.assertIn(self.coupon2_params["description"], invoice_body)  # Coupon description
+        self.assertIn("Total Discounts:", invoice_body)  # Discount section
+        self.assertIn("Subtotal:", invoice_body)  # Subtotal before discount
+        
+        # Verify the discount amount calculation
+        self.assertGreater(invoice.discount_amount_in_cents, 0, "Should have discount applied")
+        self.assertEqual(invoice.total_in_cents, 0, "Total should be $0 after $6 discount on $6 product")
+        
+        print("✓ INVOICE VERIFICATION: Coupon information correctly displayed on invoice page")
+        print(f"✓ Coupon applied: {self.coupon2_params['code']} - {self.coupon2_params['description']}")
+        print(f"✓ Discount amount: ${invoice.discount_amount_in_cents / 100:.2f}")
+        
+        # Create the user-product relationship for download testing
         from ..models.user_product import UserProduct
-        user_product = UserProduct(user=self.user2, product=product)
-        self.dbsession.add(user_product)
-        self.dbsession.flush()
+        # Check if relationship already exists from checkout completion
+        if not self.user2.can_download_product(product):
+            user_product = UserProduct(user=self.user2, product=product)
+            self.dbsession.add(user_product)
+            self.dbsession.flush()
         
         # Verify user can now download the product
         self.assertTrue(self.user2.can_download_product(product))