tests: Add cache_tries_captured helper.

zerver/lib/test_helpers.py

@@ -124,6 +124,24 @@ def capture_event(event_info: EventInfo) -> Iterator[None]:
 
     event_info.populate(m.call_args_list)
 
+@contextmanager
+def cache_tries_captured() -> Iterator[List[Tuple[str, Union[str, List[str]], Optional[str]]]]:
+    cache_queries: List[Tuple[str, Union[str, List[str]], Optional[str]]] = []
+
+    orig_get = cache.cache_get
+    orig_get_many = cache.cache_get_many
+
+    def my_cache_get(key: str, cache_name: Optional[str]=None) -> Optional[Dict[str, Any]]:
+        cache_queries.append(('get', key, cache_name))
+        return orig_get(key, cache_name)
+
+    def my_cache_get_many(keys: List[str], cache_name: Optional[str]=None) -> Dict[str, Any]:  # nocoverage -- simulated code doesn't use this
+        cache_queries.append(('getmany', keys, cache_name))
+        return orig_get_many(keys, cache_name)
+
+    with mock.patch.multiple(cache, cache_get=my_cache_get, cache_get_many=my_cache_get_many):
+        yield cache_queries
+
 @contextmanager
 def simulated_empty_cache() -> Iterator[List[Tuple[str, Union[str, List[str]], Optional[str]]]]:
     cache_queries: List[Tuple[str, Union[str, List[str]], Optional[str]]] = []

zerver/tests/test_subs.py

@@ -63,6 +63,7 @@ from zerver.lib.streams import (
 )
 from zerver.lib.test_classes import ZulipTestCase
 from zerver.lib.test_helpers import (
+    cache_tries_captured,
     get_subscription,
     most_recent_usermessage,
     queries_captured,
@@ -3289,6 +3290,7 @@ class SubscriptionAPITest(ZulipTestCase):
         test_user_ids = [user.id for user in test_users]
 
         with queries_captured() as queries:
+            with cache_tries_captured() as cache_tries:
                 with mock.patch('zerver.views.streams.send_messages_for_new_subscribers'):
                     self.common_subscribe_to_streams(
                         desdemona,
@@ -3299,6 +3301,7 @@ class SubscriptionAPITest(ZulipTestCase):
         # The only known O(N) behavior here is that we call
         # principal_to_user_profile for each of our users.
         self.assert_length(queries, 19)
+        self.assert_length(cache_tries, 28)
 
     def test_subscriptions_add_for_principal(self) -> None:
         """