diff --git a/tests/test_app.py b/tests/test_app.py
index c6da66b..7d51790 100644
--- a/tests/test_app.py
+++ b/tests/test_app.py
@@ -32,7 +32,11 @@
 }
 
 test_transposed_netcdf_store_params = {
-    "params": {"url": test_transposed_netcdf_store, "variable": "precipitation", "decode_times": False},
+    "params": {
+        "url": test_transposed_netcdf_store,
+        "variable": "precipitation",
+        "decode_times": False,
+    },
     "variables": ["precipitation"],
 }
 
@@ -169,7 +173,7 @@ def test_get_tilejson_pyramid(app):
 
 def get_tile_test(app, ds_params, zoom: int = 0):
     response = app.get(
-        f"/tiles/0/0/0.png",
+        "/tiles/0/0/0.png",
         params=ds_params["params"],
     )
     assert response.status_code == 200
@@ -192,6 +196,7 @@ def test_get_tile_reference(app):
 def test_get_tile_netcdf(app):
     return get_tile_test(app, test_netcdf_store_params)
 
+
 def test_get_tile_transposed_netcdf(app):
     return get_tile_test(app, test_transposed_netcdf_store_params)
 
diff --git a/titiler/xarray/reader.py b/titiler/xarray/reader.py
index b41577f..f42e0df 100644
--- a/titiler/xarray/reader.py
+++ b/titiler/xarray/reader.py
@@ -138,7 +138,7 @@ def xarray_open_dataset(
     xr_open_args: Dict[str, Any] = {
         "decode_coords": "all",
         "decode_times": decode_times,
-        "engine": xr_engine
+        "engine": xr_engine,
     }
 
     # Argument if we're opening a datatree