diff --git a/tests/test_calcat_interface2.py b/tests/test_calcat_interface2.py
index 40cf16b4109df2d630397d13fac9b707b7676ffa..6159e80c965041900a83135c3cd5ab0073e64bea 100644
--- a/tests/test_calcat_interface2.py
+++ b/tests/test_calcat_interface2.py
@@ -25,7 +25,7 @@ def test_AGIPD_CalibrationData_metadata():
         calibrations=['Offset', 'SlopesFF'],
     )
     assert 'Offset' in agipd_cd
-    assert set(agipd_cd['Offset'].constants) == {'AGIPD{i:02}' for i in range(16)}
+    assert set(agipd_cd['Offset'].constants) == {f'AGIPD{i:02}' for i in range(16)}
     assert isinstance(agipd_cd['Offset'].constants['AGIPD00'], SingleConstantVersion)
 
 
@@ -48,7 +48,7 @@ def test_AGIPD_CalibrationData_metadata_SPB():
         event_at="2020-01-07 13:26:48.00",
     )
     assert 'Offset' in agipd_cd
-    assert set(agipd_cd['Offset'].constants) == {'AGIPD{i:02}' for i in range(16)}
+    assert set(agipd_cd['Offset'].constants) == {f'AGIPD{i:02}' for i in range(16)}
     assert isinstance(agipd_cd['Offset'].constants['AGIPD00'], SingleConstantVersion)