diff --git a/tests/test_iot/test_iot.py b/tests/test_iot/test_iot.py
index f3c151714..2f43de5b9 100644
--- a/tests/test_iot/test_iot.py
+++ b/tests/test_iot/test_iot.py
@@ -729,13 +729,14 @@ def test_principal_thing():
     res.should.have.key("principals").which.should.have.length_of(0)
 
     with assert_raises(ClientError) as e:
-        client.list_thing_principals(thingName='xxx')
+        client.list_thing_principals(thingName="xxx")
 
     e.exception.response["Error"]["Code"].should.equal("ResourceNotFoundException")
     e.exception.response["Error"]["Message"].should.equal(
         "Failed to list principals for thing xxx because the thing does not exist in your account"
     )
 
+
 @mock_iot
 def test_delete_principal_thing():
     client = boto3.client("iot", region_name="ap-northeast-1")