PB-1109 Return 400 instead of 404 when FK nonexistent

app/access/api.py

@@ -114,8 +114,8 @@ def update_user(
 
     Return HTTP status code
     - 200 (OK) if the user has been updated successfully
-    - 404 (Not Found) if there is no user with the given username or if there is
-      no provider with the given ID
+    - 400 (Bad Request) if there is no provider with the given ID
+    - 404 (Not Found) if there is no user with the given username
     - 500 (Internal Server Error) if there is an inconsistency with Cognito
     - 503 (Service Unavailable) if Cognito cannot be reached
     """
@@ -125,7 +125,7 @@ def update_user(
             raise Http404()
 
         if not Provider.objects.filter(id=user_in.provider_id).exists():
-            raise HttpError(HTTPStatus.NOT_FOUND, "Provider does not exist")
+            raise HttpError(HTTPStatus.BAD_REQUEST, "Provider does not exist")
 
         for attr, value in user_in.dict(exclude_unset=True).items():
             setattr(user_object, attr, value)

app/access/tests/test_api.py

@@ -346,7 +346,7 @@ def test_update_user_returns_404_and_leaves_user_as_is_if_user_nonexistent(self)
         user_after = User.objects.filter(username="dude").first()
         assert user_after == user_before
 
-    def test_update_user_returns_404_and_leaves_user_as_is_if_provider_nonexistent(self):
+    def test_update_user_returns_400_and_leaves_user_as_is_if_provider_nonexistent(self):
 
         user_before = User.objects.filter(username="dude").first()
         nonexistent_id = Provider.objects.last().id + 1234
@@ -360,8 +360,8 @@ def test_update_user_returns_404_and_leaves_user_as_is_if_provider_nonexistent(s
 
         response = self.client.put("users/dude", json=payload)
 
-        assert response.status_code == 404
-        assert response.data == {"code": 404, "description": "Provider does not exist"}
+        assert response.status_code == 400
+        assert response.data == {"code": 400, "description": "Provider does not exist"}
         user_after = User.objects.filter(username="dude").first()
         assert user_after == user_before