diff --git a/tests/helpers/tests/test_assertions.py b/tests/helpers/tests/test_assertions.py
index d597f06ae..864f723a4 100644
--- a/tests/helpers/tests/test_assertions.py
+++ b/tests/helpers/tests/test_assertions.py
@@ -3,6 +3,7 @@
 
 import io
 import wave
+from contextlib import nullcontext
 from types import SimpleNamespace
 
 import numpy as np