diff --git a/tests/test_register_custom_ops.py b/tests/test_register_custom_ops.py
index e47104c3a..7c11b45a3 100644
--- a/tests/test_register_custom_ops.py
+++ b/tests/test_register_custom_ops.py
@@ -60,9 +60,11 @@ class Distance(PairOperator):
         series_right = self.feature_right.load(instrument, start_index, end_index, freq)
         return np.abs(series_left - series_right)
 
+
 OpsList = [Diff, Distance]
 Operators.register(OpsList)
 
+
 class TestRegiterCustomOps(TestAutoData):
     def test_regiter_custom_ops(self):
         instruments = ["SH600000"]