user-groups: Send delete user group event.

Fixes #7380

zerver/lib/actions.py

@@ -4362,6 +4362,13 @@ def remove_members_from_user_group(user_group, user_profiles):
     user_ids = [up.id for up in user_profiles]
     do_send_user_group_members_update_event('remove_members', user_group, user_ids)
 
+def do_send_delete_user_group_event(user_group_id: int, realm_id: int) -> None:
+    event = dict(type="user_group",
+                 op="remove",
+                 group_id=user_group_id)
+    send_event(event, active_user_ids(realm_id))
+
 def check_delete_user_group(user_group_id: int, realm: Realm) -> None:
     user_group = access_user_group_by_id(user_group_id, realm)
     user_group.delete()
+    do_send_delete_user_group_event(user_group_id, realm.id)

zerver/lib/events.py

@@ -571,6 +571,9 @@ def apply_event(state, event, user_profile, client_gravatar, include_subscribers
                     members = set(user_group['members'])
                     user_group['members'] = list(members - set(event['user_ids']))
                     user_group['members'].sort()
+        elif event['op'] == 'remove':
+            state['realm_user_groups'] = [ug for ug in state['realm_user_groups']
+                                          if ug['id'] != event['group_id']]
     else:
         raise AssertionError("Unexpected event type %s" % (event['type'],))
 

zerver/tests/test_events.py

@@ -80,6 +80,7 @@ from zerver.lib.actions import (
     do_update_user_group_description,
     bulk_add_members_to_user_group,
     remove_members_from_user_group,
+    check_delete_user_group,
 )
 from zerver.lib.events import (
     apply_events,
@@ -1061,6 +1062,16 @@ class EventsRegisterTest(ZulipTestCase):
         error = user_group_remove_member_checker('events[0]', events[0])
         self.assert_on_error(error)
 
+        # Test delete event
+        user_group_remove_checker = self.check_events_dict([
+            ('type', equals('user_group')),
+            ('op', equals('remove')),
+            ('group_id', check_int),
+        ])
+        events = self.do_test(lambda: check_delete_user_group(backend.id, backend.realm))
+        error = user_group_remove_checker('events[0]', events[0])
+        self.assert_on_error(error)
+
     def test_default_stream_groups_events(self):
         # type: () -> None
         default_stream_groups_checker = self.check_events_dict([