diff --git a/tests/server.py b/tests/server.py
index 79f08313e8..7e2fcb6f08 100644
--- a/tests/server.py
+++ b/tests/server.py
@@ -637,6 +637,10 @@ class ThreadedMemoryReactorClock:
         self.triggers[key] = (callable, args)
         return key
 
+    def removeSystemEventTrigger(self, trigger_id: Any) -> None:
+        """Remove a previously registered system event trigger."""
+        self.triggers.pop(trigger_id, None)
+
     def getThreadPool(self) -> Any:
         return self.threadpool
 
diff --git a/tests/unittest.py b/tests/unittest.py
index 248dfe81eb..ec581318c9 100644
--- a/tests/unittest.py
+++ b/tests/unittest.py
@@ -576,6 +576,21 @@ class HomeserverTestCase(TestCase):
             if inspect.isawaitable(res):
                 await res
 
+    async def asyncTearDown(self) -> None:
+        """Shut down the homeserver to cancel all background tasks.
+
+        This prevents looping calls and delayed calls from firing during
+        cleanup, which would leave non-sentinel logging contexts active
+        and cause the next test's setUp to fail.
+        """
+        if hasattr(self, 'hs') and self.hs is not None:
+            self.hs.get_clock().shutdown()
+            # Give event loop time for cancellation to propagate
+            await asyncio.sleep(0)
+            await asyncio.sleep(0)
+        # Ensure we're back in the sentinel context
+        set_current_context(SENTINEL_CONTEXT)
+
     def tearDown(self) -> None:
         # Reset to not use frozen dicts.
         events.USE_FROZEN_DICTS = False