Reintroduce #17291. (#17338)

This is #17291 (which got reverted), with some added fixups, and change
so that tests actually pick up the error.

The problem was that we were not calculating any new chain IDs due to a
missing `not` in a condition.

1 files changed, 2 insertions, 0 deletions

diff --git a/tests/unittest.py b/tests/unittest.py
index 18963b9e32..a7c20556a0 100644
--- a/tests/unittest.py
+++ b/tests/unittest.py
@@ -344,6 +344,8 @@ class HomeserverTestCase(TestCase):
         self._hs_args = {"clock": self.clock, "reactor": self.reactor}
         self.hs = self.make_homeserver(self.reactor, self.clock)
 
+        self.hs.get_datastores().main.tests_allow_no_chain_cover_index = False
+
         # Honour the `use_frozen_dicts` config option. We have to do this
         # manually because this is taken care of in the app `start` code, which
         # we don't run. Plus we want to reset it on tearDown.