event_schema: Add checker for restart event.

Part of #17568.

frontend_tests/node_tests/lib/events.js

@@ -479,6 +479,7 @@ exports.fixtures = {
 
     restart: {
         type: "restart",
+        server_generation: 2,
         immediate: true,
     },
 

zerver/lib/event_schema.py

@@ -1085,6 +1085,11 @@ def check_realm_user_update(
     )
 
 
+restart_event = event_dict_type(
+    required_keys=[("type", Equals("restart")), ("server_generation", int), ("immediate", bool)]
+)
+check_restart_event = make_checker(restart_event)
+
 stream_create_event = event_dict_type(
     required_keys=[
         ("type", Equals("stream")),

zerver/tests/test_event_system.py

@@ -7,6 +7,7 @@ from django.conf import settings
 from django.http import HttpRequest, HttpResponse
 
 from zerver.lib.actions import check_send_message, do_change_user_role, do_set_realm_property
+from zerver.lib.event_schema import check_restart_event
 from zerver.lib.events import fetch_initial_state_data, get_raw_user_data
 from zerver.lib.test_classes import ZulipTestCase
 from zerver.lib.test_helpers import HostRequestMock, queries_captured, stub_event_queue_user_events
@@ -816,9 +817,7 @@ class RestartEventsTest(ZulipTestCase):
         self.assertEqual(len(virtual_events), 1)
         restart_event = virtual_events["restart"]
 
-        # TODO: add a schema checker for this to event_schema.py
-        # and exercise it here (as well as the more concrete
-        # check)
+        check_restart_event("restart_event", restart_event)
         self.assertEqual(
             restart_event,
             dict(