tests: Avoid unchecked casts.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

zerver/lib/test_classes.py

@@ -5,7 +5,7 @@ import shutil
 import tempfile
 import urllib
 from contextlib import contextmanager
-from typing import Any, Dict, Iterable, Iterator, List, Optional, Sequence, Set, Tuple, Union, cast
+from typing import Any, Dict, Iterable, Iterator, List, Optional, Sequence, Set, Tuple, Union
 from unittest import mock
 
 import ujson
@@ -41,6 +41,7 @@ from zerver.lib.streams import (
 )
 from zerver.lib.test_helpers import find_key_by_email, instrument_url
 from zerver.lib.users import get_api_key
+from zerver.lib.validator import check_string
 from zerver.lib.webhooks.common import get_fixture_http_headers, standardize_headers
 from zerver.models import (
     Client,
@@ -543,7 +544,10 @@ class ZulipTestCase(TestCase):
         subs = get_stream_subscriptions_for_user(user_profile).filter(
             active=True,
         )
-        return [cast(str, get_display_recipient(sub.recipient)) for sub in subs]
+        return [
+            check_string("recipient", get_display_recipient(sub.recipient))
+            for sub in subs
+        ]
 
     def send_personal_message(self, from_user: UserProfile, to_user: UserProfile, content: str="test content",
                               sending_client_name: str="test suite") -> int:

zerver/tests/test_tornado.py

@@ -1,5 +1,5 @@
 import urllib.parse
-from typing import Any, Dict, List, Optional, cast
+from typing import Any, Dict, Optional
 
 import ujson
 from django.conf import settings
@@ -114,8 +114,7 @@ class EventsTestCase(TornadoWebTestCase):
         self.io_loop.call_later(0.1, process_events)
         response = self.wait()
         data = ujson.loads(response.body)
-        events = data['events']
-        events = cast(List[Dict[str, Any]], events)
-        self.assertEqual(len(events), 1)
-        self.assertEqual(events[0]['data'], 'test data')
+        self.assertEqual(data['events'], [
+            {'type': 'test', 'data': 'test data', 'id': 0},
+        ])
         self.assertEqual(data['result'], 'success')