diff --git a/registrasion/tests/cart_controller_helper.py b/registrasion/tests/controller_helpers.py
similarity index 100%
rename from registrasion/tests/cart_controller_helper.py
rename to registrasion/tests/controller_helpers.py
diff --git a/registrasion/tests/test_cart.py b/registrasion/tests/test_cart.py
index d47d659e135c37f26ded6ec06922f11db942290e..10ba10d212bfbdf8fed9903f017612ac624dc335 100644
--- a/registrasion/tests/test_cart.py
+++ b/registrasion/tests/test_cart.py
@@ -10,7 +10,7 @@ from django.test import TestCase
 from registrasion import models as rego
 from registrasion.controllers.product import ProductController
 
-from cart_controller_helper import TestingCartController
+from controller_helpers import TestingCartController
 from patch_datetime import SetTimeMixin
 
 UTC = pytz.timezone('UTC')
diff --git a/registrasion/tests/test_ceilings.py b/registrasion/tests/test_ceilings.py
index f8481fea015d9d60d5e55a3874baf0584d00d3ad..c566448103c0cfe328eba42778bcbf952910c4c8 100644
--- a/registrasion/tests/test_ceilings.py
+++ b/registrasion/tests/test_ceilings.py
@@ -3,7 +3,7 @@ import pytz
 
 from django.core.exceptions import ValidationError
 
-from cart_controller_helper import TestingCartController
+from controller_helpers import TestingCartController
 from test_cart import RegistrationCartTestCase
 
 from registrasion import models as rego
diff --git a/registrasion/tests/test_enabling_condition.py b/registrasion/tests/test_enabling_condition.py
index 5d0e410c911dfd4a21fb56a688081fc3c66eda52..d977cc5ceb74c1abbe2f11326c4e30b849bc611a 100644
--- a/registrasion/tests/test_enabling_condition.py
+++ b/registrasion/tests/test_enabling_condition.py
@@ -4,7 +4,7 @@ from django.core.exceptions import ValidationError
 
 from registrasion import models as rego
 from registrasion.controllers.category import CategoryController
-from cart_controller_helper import TestingCartController
+from controller_helpers import TestingCartController
 from registrasion.controllers.product import ProductController
 
 from test_cart import RegistrationCartTestCase
diff --git a/registrasion/tests/test_invoice.py b/registrasion/tests/test_invoice.py
index 19332392913d493add3412cbe604d79bc78bdd0e..080ca008e748c76ada66d42eb6308bb48ffb8617 100644
--- a/registrasion/tests/test_invoice.py
+++ b/registrasion/tests/test_invoice.py
@@ -5,7 +5,7 @@ from decimal import Decimal
 from django.core.exceptions import ValidationError
 
 from registrasion import models as rego
-from cart_controller_helper import TestingCartController
+from controller_helpers import TestingCartController
 from registrasion.controllers.invoice import InvoiceController
 
 from test_cart import RegistrationCartTestCase
@@ -197,4 +197,11 @@ class InvoiceTestCase(RegistrationCartTestCase):
     def test_cannot_generate_blank_invoice(self):
         current_cart = TestingCartController.for_user(self.USER_1)
         with self.assertRaises(ValidationError):
-            InvoiceController.for_cart(current_cart.cart)
+            invoice_1 = InvoiceController.for_cart(current_cart.cart)
+
+    # TODO: test partially paid invoice cannot be void until payments
+    # are refunded
+
+    # TODO: test overpaid invoice results in credit note
+
+    # TODO: test credit note generation more generally 
diff --git a/registrasion/tests/test_refund.py b/registrasion/tests/test_refund.py
index bde25929c77a0054ceee5e14cbd4be6ebdb09abf..e0b6c6812d168a23eb23077b17c61d757ea91ede 100644
--- a/registrasion/tests/test_refund.py
+++ b/registrasion/tests/test_refund.py
@@ -1,6 +1,6 @@
 import pytz
 
-from cart_controller_helper import TestingCartController
+from controller_helpers import TestingCartController
 from registrasion.controllers.invoice import InvoiceController
 
 from test_cart import RegistrationCartTestCase
diff --git a/registrasion/tests/test_voucher.py b/registrasion/tests/test_voucher.py
index a8bc6b00f5c16c3e27e9c5f7e5f500bebda5d2f9..443ce1d71a331a8605465396c4e0b1eb12ff423a 100644
--- a/registrasion/tests/test_voucher.py
+++ b/registrasion/tests/test_voucher.py
@@ -6,7 +6,7 @@ from django.core.exceptions import ValidationError
 from django.db import IntegrityError
 
 from registrasion import models as rego
-from cart_controller_helper import TestingCartController
+from controller_helpers import TestingCartController
 from registrasion.controllers.invoice import InvoiceController
 
 from test_cart import RegistrationCartTestCase