Add redis "barrier" in cleanup_keys

To prevent pytest-xdist workers stomping each other with _delete_test_keys

tests/conftest.py

@@ -37,11 +37,18 @@ def key_prefix(request, redis):
 
 @pytest.fixture(scope="session", autouse=True)
 def cleanup_keys(request):
-    def cleanup_keys():
     # Always use the sync Redis connection with finalizer. Setting up an
     # async finalizer should work, but I'm not suer how yet!
     from redis_om.connections import get_redis_connection as get_sync_redis
 
-        _delete_test_keys(TEST_PREFIX, get_sync_redis())
+    # Increment for every pytest-xdist worker
+    redis = get_sync_redis()
+    once_key = f"{TEST_PREFIX}:cleanup_keys"
+    redis.incr(once_key)
 
-    request.addfinalizer(cleanup_keys)
+    yield
+
+    # Delete keys only once
+    if redis.decr(once_key) == 0:
+        _delete_test_keys(TEST_PREFIX, redis)
+        redis.delete(once_key)