user groups: Test query counts for adding group members.

The most expensive thing for adding user groups is sending
all the notification messages, but we at least want to make
sure that the basic stuff runs in constant time.

zerver/tests/test_user_groups.py

@@ -6,8 +6,13 @@ import orjson
 from django.utils.timezone import now as timezone_now
 
 from zerver.actions.realm_settings import do_set_realm_property
-from zerver.actions.user_groups import check_add_user_group, promote_new_full_members
+from zerver.actions.user_groups import (
+    check_add_user_group,
+    create_user_group_in_database,
+    promote_new_full_members,
+)
 from zerver.actions.users import do_deactivate_user
+from zerver.lib.create_user import create_user
 from zerver.lib.mention import silent_mention_syntax_for_user
 from zerver.lib.streams import ensure_stream
 from zerver.lib.test_classes import ZulipTestCase
@@ -586,6 +591,58 @@ class UserGroupAPITestCase(UserGroupTestCase):
         result = self.client_delete(f"/json/user_groups/{lear_test_group.id}")
         self.assert_json_error(result, "Invalid user group")
 
+    def test_query_counts(self) -> None:
+        hamlet = self.example_user("hamlet")
+        cordelia = self.example_user("cordelia")
+        realm = hamlet.realm
+        self.login_user(hamlet)
+
+        original_users = [
+            create_user(
+                email=f"original_user{i}@zulip.com",
+                password=None,
+                realm=realm,
+                full_name="full_name",
+            )
+            for i in range(50)
+        ]
+
+        with self.assert_database_query_count(4):
+            user_group = create_user_group_in_database(
+                name="support",
+                members=[hamlet, cordelia, *original_users],
+                realm=realm,
+                acting_user=hamlet,
+            )
+
+        self.assert_user_membership(user_group, [hamlet, cordelia, *original_users])
+
+        new_users = [
+            create_user(
+                email=f"new_user{i}@zulip.com",
+                password=None,
+                realm=realm,
+                full_name="full_name",
+            )
+            for i in range(50)
+        ]
+
+        new_user_ids = [user.id for user in new_users]
+
+        munge = lambda obj: orjson.dumps(obj).decode()
+        params = dict(add=munge(new_user_ids))
+
+        with mock.patch("zerver.views.user_groups.notify_for_user_group_subscription_changes"):
+            with self.assert_database_query_count(11):
+                result = self.client_post(f"/json/user_groups/{user_group.id}/members", info=params)
+        self.assert_json_success(result)
+
+        with self.assert_database_query_count(1):
+            all_user_ids = get_user_group_member_ids(user_group, direct_member_only=True)
+
+        self.assert_length(all_user_ids, 102)
+        self.assert_user_membership(user_group, [hamlet, cordelia, *new_users, *original_users])
+
     def test_update_members_of_user_group(self) -> None:
         hamlet = self.example_user("hamlet")
         self.login("hamlet")