diff --git a/src/legendhpges/base.py b/src/legendhpges/base.py
index 0f95e95..6dbc45e 100644
--- a/src/legendhpges/base.py
+++ b/src/legendhpges/base.py
@@ -220,4 +220,6 @@ def surface_area(self, surface_indices: list | None = None) -> Quantity:
             r = r[surface_indices]
             z = z[surface_indices]
 
-        return np.sum(np.where(dr == 0, abs(dz) * r[:-1] * 2 * np.pi, abs(dr) * dl * np.pi))
+        return np.sum(
+            np.where(dr == 0, abs(dz) * r[:-1] * 2 * np.pi, abs(dr) * dl * np.pi)
+        )
diff --git a/tests/test_det_properties.py b/tests/test_det_properties.py
index e783977..c2dbdeb 100644
--- a/tests/test_det_properties.py
+++ b/tests/test_det_properties.py
@@ -2,7 +2,6 @@
 
 import pathlib
 
-import numpy as np
 import pytest
 from legendmeta import TextDB
 from legendtestdata import LegendTestData
@@ -29,6 +28,5 @@ def test_surface_area(test_data_configs):
     reg = geant4.Registry()
     gedet = make_hpge(test_data_configs + "/C99000A.json", registry=reg)
 
-    assert gedet.surface_area(surface_indices=[])==0
-    assert gedet.surface_area(surface_indices=None)>0
-
+    assert gedet.surface_area(surface_indices=[]) == 0
+    assert gedet.surface_area(surface_indices=None) > 0