diff --git a/backend/app/main.py b/backend/app/main.py
index aa051a98..4133255b 100644
--- a/backend/app/main.py
+++ b/backend/app/main.py
@@ -82,7 +82,7 @@ async def update_plan(
     )
     return AssignmentsUpdate(
         acknowledged=result.acknowledged,
-        inserted_id=result.upserted_id,
+        upserted_id=result.upserted_id,
         matched_count=result.matched_count,
         modified_count=result.modified_count,
     )
diff --git a/backend/app/models.py b/backend/app/models.py
index a03e5b53..366932e2 100644
--- a/backend/app/models.py
+++ b/backend/app/models.py
@@ -70,7 +70,7 @@ class AssignmentsUpdate(BaseModel):
     """
 
     acknowledged: bool = PydanticField(description="Acknowledged")
-    inserted_id: Optional[str] = PydanticField(description="Inserted ID")
+    upserted_id: Optional[str] = PydanticField(description="Inserted ID")
     matched_count: int = PydanticField(description="Matched count")
     modified_count: int = PydanticField(description="Modified count")
 
diff --git a/backend/app/test_main.py b/backend/app/test_main.py
index fd5beefc..eb3c8edc 100644
--- a/backend/app/test_main.py
+++ b/backend/app/test_main.py
@@ -58,7 +58,6 @@ def plan_id_fixture() -> InsertOneResult:
 
 
 def test_get_plan(client: TestClient, plan: InsertOneResult):
-    print(plan.inserted_id)
     response = client.get(f"/plan/{plan.inserted_id}")
     assert response.status_code == 200
 
@@ -68,18 +67,17 @@ def test_create_plan(client: TestClient):
     assert response.status_code == 201
 
 
-def test_update_plan(client: TestClient, plan: InsertOneResult):
+def test_update_add_to_plan(client: TestClient, plan: InsertOneResult):
     response = client.put(
         f"/plan/{plan.inserted_id}", json={"assignments": {"06067001102": 1}}
     )
     assert response.status_code == 200
     data = response.json()
     assert data["modified_count"] == 1
+    assert data["upserted_id"] is None
 
 
-def test_update_plan_with_modification_to_existing_assignment(
-    client: TestClient, plan: InsertOneResult
-):
+def test_update_update_and_add(client: TestClient, plan: InsertOneResult):
     response = client.put(
         f"/plan/{plan.inserted_id}",
         json={"assignments": {"06067001101": 2, "06067001102": 1}},
@@ -87,6 +85,9 @@ def test_update_plan_with_modification_to_existing_assignment(
     assert response.status_code == 200
     data = response.json()
     assert data["modified_count"] == 1
+    assert data["matched_count"] == 1
+    assert data["acknowledged"] is True
+    assert data["upserted_id"] is None
 
 
 def test_get_missing_plan(client: TestClient):