Add another test showing the weak ref metadata not growing unchecked

tests/storage/databases/main/test_events_worker.py

@@ -273,6 +273,41 @@ def test_event_ref(self) -> None:
             # from the DB
             self.assertEqual(ctx.get_resource_usage().evt_db_fetch_count, 0)
 
+    def test_invalidating_get_event_cache_also_removes_metadata(self) -> None:
+        """
+        Test that when an event is removed from the get_event_cache, that the associated
+        entries in the metadata cache are also removed.
+        """
+        # Reset the event cache
+        self.store._get_event_cache.clear()
+
+        # Retrieve the event base though we never use it. This will populate the caches
+        event_base = self.get_success(self.store.get_event(self.event_id))  # noqa: F841
+
+        self.assertIsNotNone(event_base)
+        cache_entry_1 = self.store._get_event_cache.get_local((self.event_id,), None)
+        self.assertIsNotNone(cache_entry_1)
+
+        cache_entry_2 = self.store._event_metadata[self.room].events.get(self.event_id, None)
+        self.assertIsNotNone(cache_entry_2)
+
+        # These are the same EventCacheEntry
+        self.assertIs(cache_entry_1, cache_entry_2)
+
+        # Remove the reference, so they won't hang around accidentally.
+        del cache_entry_1
+        del cache_entry_2
+
+        # Remove *only* the event in the get_event_cache(and of course the event_ref and
+        # current_fetches) but don't directly touch the metadata cache.
+        self.store._invalidate_local_get_event_cache(self.event_id)
+
+        # Let's see what is in the metadata cache at this point
+        cache_entry_3 = self.store._event_metadata[self.room].events.get(self.event_id, None)
+
+        # Poof! It's gone.
+        self.assertIsNone(cache_entry_3)
+
     def test_dedupe(self) -> None:
         """Test that if we request the same event multiple times we only pull it
         out once.