Fix case in `wait_for_background_updates` where `self.store` does not exist (#11331)

Pull the DataStore from the HomeServer instance, which
always exists.

2 files changed, 5 insertions, 7 deletions

diff --git a/changelog.d/11331.misc b/changelog.d/11331.misc
new file mode 100644
index 0000000000..1ab3a6a975
--- /dev/null
+++ b/changelog.d/11331.misc
@@ -0,0 +1 @@
+A test helper (`wait_for_background_updates`) no longer depends on classes defining a `store` property.
diff --git a/tests/unittest.py b/tests/unittest.py
index eea0903f05..1431848367 100644
--- a/tests/unittest.py
+++ b/tests/unittest.py
@@ -331,16 +331,13 @@ class HomeserverTestCase(TestCase):
             time.sleep(0.01)
 
     def wait_for_background_updates(self) -> None:
-        """Block until all background database updates have completed.
-
-        Note that callers must ensure there's a store property created on the
-        testcase.
-        """
+        """Block until all background database updates have completed."""
+        store = self.hs.get_datastore()
         while not self.get_success(
-            self.store.db_pool.updates.has_completed_background_updates()
+            store.db_pool.updates.has_completed_background_updates()
         ):
             self.get_success(
-                self.store.db_pool.updates.do_next_background_update(False), by=0.1
+                store.db_pool.updates.do_next_background_update(False), by=0.1
             )
 
     def make_homeserver(self, reactor, clock):