diff --git a/tosfs/tests/test_fsspec_integration.py b/tosfs/tests/test_fsspec_integration.py
index 54c2ed9..120839c 100644
--- a/tosfs/tests/test_fsspec_integration.py
+++ b/tosfs/tests/test_fsspec_integration.py
@@ -84,7 +84,7 @@ def __init__(self):
 
 def test_customized_class(bucket, temporary_workspace):
     # clear firstly
-    known_implementations["tos"] = { "class": ""}
+    known_implementations["tos"] = {"class": ""}
     known_implementations["tos"] = {
         "class": "tosfs.tests.test_fsspec_integration.MyTosFileSystem"
     }