diff --git a/stix2/test/v21/test_external_reference.py b/stix2/test/v21/test_external_reference.py
index 03cf928..f347191 100644
--- a/stix2/test/v21/test_external_reference.py
+++ b/stix2/test/v21/test_external_reference.py
@@ -128,6 +128,6 @@ def test_external_reference_bad_hash():
             source_name="ACME Threat Intel",
             description="Threat report",
             hashes={
-                "SHA-123": "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
-            }
-        )
\ No newline at end of file
+                "SHA-123": "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
+            },
+        )