chore(): test and validation improvements

src/backend/apps/reviews/services.py

@@ -1,5 +1,6 @@
 from typing import Any
 
+from config.errors import ConflictError
 from django.core.exceptions import ValidationError
 from django.db import transaction
 
@@ -91,13 +92,15 @@ def approver_group_create(
 ) -> ApproverGroup:
     _validate_experimenter(experimenter)
     if ApproverGroup.objects.filter(experimenter=experimenter).exists():
-        raise ValidationError(
-            {
-                "experimenter": (
-                    f"An approver group already exists for "
-                    f"experimenter '{experimenter.username}'."
-                )
-            }
+        raise ConflictError(
+            ValidationError(
+                {
+                    "experimenter": (
+                        f"An approver group already exists for "
+                        f"experimenter '{experimenter.username}'."
+                    )
+                }
+            )
         )
     approvers: list[User] = []
     if approver_ids:

src/backend/apps/reviews/tests/test_reviews_approver_groups.py

@@ -14,6 +14,7 @@ from apps.reviews.selectors import (
     approver_group_list_for_approver,
 )
 from apps.reviews.services import (
+    ConflictError,
     approver_group_add_approver,
     approver_group_create,
     approver_group_delete,
@@ -73,7 +74,7 @@ class ApproverGroupModelTest(TestCase):
 
     def test_one_to_one_constraint(self) -> None:
         approver_group_create(experimenter=self.experimenter)
-        with self.assertRaises(ValidationError):
+        with self.assertRaises(ConflictError):
             approver_group_create(
                 experimenter=self.experimenter,
                 min_approvals=1,
@@ -148,7 +149,7 @@ class ApproverGroupCreateServiceTest(TestCase):
 
     def test_create_rejects_duplicate_group(self) -> None:
         approver_group_create(experimenter=self.experimenter)
-        with self.assertRaises(ValidationError):
+        with self.assertRaises(ConflictError):
             approver_group_create(experimenter=self.experimenter)
 
     def test_create_min_approvals_zero_raises(self) -> None:

src/backend/apps/users/admin.py

@@ -13,12 +13,12 @@ class UserAdmin(BaseUserAdmin):
         User.role.field.name,
         User.first_name.field.name,
         User.last_name.field.name,
-        User._meta.get_field("is_active").name,
+        User.is_active.field.name,
         User.is_staff.field.name,
     )
     list_filter = (
         User.role.field.name,
-        User._meta.get_field("is_active").name,
+        User.is_active.field.name,
         User.is_staff.field.name,
         User.is_superuser.field.name,
     )
@@ -56,7 +56,7 @@ class UserAdmin(BaseUserAdmin):
             _("Permissions"),
             {
                 "fields": (
-                    User._meta.get_field("is_active").name,
+                    User.is_active.field.name,
                     User.is_staff.field.name,
                     User.is_superuser.field.name,
                     User.groups.field.name,