diff --git a/usage_function/tests/test_utils.py b/usage_function/tests/test_utils.py
index 2c4b1dd..6ec4090 100644
--- a/usage_function/tests/test_utils.py
+++ b/usage_function/tests/test_utils.py
@@ -308,6 +308,79 @@ def test_combine_items(self) -> None:
         )
         self.assertEqual(expected, existing_item)
 
+    def test_combine_itemz_1(self) -> None:
+        """Check that we sum the costs."""
+        items_a = [
+            models.Usage(
+                id="someid",
+                date=date.today(),
+                cost=1,
+                total_cost=1,
+                subscription_id=UUID(int=0),
+            ),
+            models.Usage(
+                id="someid",
+                date=date.today(),
+                cost=1,
+                total_cost=1,
+                subscription_id=UUID(int=0),
+            ),
+        ]
+
+        actual = utils.usage.combine_itemz(items_a)
+
+        expected = [
+            models.Usage(
+                id="someid",
+                date=date.today(),
+                cost=2,
+                total_cost=2,
+                subscription_id=UUID(int=0),
+            ),
+        ]
+        self.assertListEqual(expected, actual)
+
+    def test_combine_itemz_2(self) -> None:
+        """Check that we sum the costs."""
+        items_a = [
+            models.Usage(
+                id="someid",
+                date=date.today(),
+                cost=1,
+                total_cost=1,
+                subscription_id=UUID(int=0),
+                reservation_id="somereservation",
+            ),
+            models.Usage(
+                id="someid",
+                date=date.today(),
+                cost=1,
+                total_cost=1,
+                subscription_id=UUID(int=0),
+            ),
+        ]
+
+        actual = utils.usage.combine_itemz(items_a)
+
+        expected = [
+            models.Usage(
+                id="someid",
+                date=date.today(),
+                cost=1,
+                total_cost=1,
+                subscription_id=UUID(int=0),
+                reservation_id="somereservation",
+            ),
+            models.Usage(
+                id="someid",
+                date=date.today(),
+                cost=1,
+                total_cost=1,
+                subscription_id=UUID(int=0),
+            ),
+        ]
+        self.assertListEqual(expected, actual)
+
 
 class TestSettings(TestCase):
     """Tests for the utils.settings module."""
diff --git a/usage_function/utils/usage.py b/usage_function/utils/usage.py
index 4dd4b65..8173899 100644
--- a/usage_function/utils/usage.py
+++ b/usage_function/utils/usage.py
@@ -103,6 +103,11 @@ def combine_items(item_to_update: models.Usage, other_item: models.Usage) -> Non
     item_to_update.cost += other_item.cost
 
 
+def combine_itemz(a):
+    """Sample docstring."""
+    pass
+
+
 def retrieve_usage(
     usage_data: Iterable[UsageDetailsListResult],
 ) -> list[models.Usage]:
@@ -116,7 +121,7 @@ def retrieve_usage(
     """
     logging.warning("Retrieve items")
 
-    all_items: Dict[str, models.Usage] = {}
+    all_items: Dict[str, list[models.Usage]] = {}
     started_processing_at = datetime.now()
 
     for i, item in enumerate(usage_data):