test_freeze fails, possibly due to race condition

tests/test_system_models.py

@@ -1,6 +1,6 @@
 import unittest
 from datetime import date
-
+from time import sleep
 import os
 import shutil
 from infi.clickhouse_orm.database import Database
@@ -61,6 +61,7 @@ class SystemPartTest(unittest.TestCase):
         # There can be other backups in the folder
         prev_backups = set(self._get_backups())
         parts[0].freeze()
+        sleep(1)
         backups = set(self._get_backups())
         self.assertEqual(len(backups), len(prev_backups) + 1)
         # Clean created backup