diff --git a/tests/test_single_obs_key.py b/tests/test_single_obs_key.py
index 22130db..cb74948 100644
--- a/tests/test_single_obs_key.py
+++ b/tests/test_single_obs_key.py
@@ -1,6 +1,8 @@
 from ase.build import molecule
+
 import znh5md
 
+
 def test_single_obs_key_info(tmp_path):
     # Test a special case where only the first config has the key
     # which caused an error in the past
@@ -12,4 +14,4 @@ def test_single_obs_key_info(tmp_path):
     io.extend([water for _ in range(5)])
     assert len(io) == 6
     assert len(io[:]) == 6
-    assert len(list(io)) == 6
\ No newline at end of file
+    assert len(list(io)) == 6