diff --git a/xarray/backends/zarr.py b/xarray/backends/zarr.py
index 98936aae31a..c66cd65e4ad 100644
--- a/xarray/backends/zarr.py
+++ b/xarray/backends/zarr.py
@@ -112,7 +112,9 @@ def __getitem__(self, key):
         # could possibly have a work-around for 0d data here
 
 
-def _determine_zarr_chunks(enc_chunks, var_chunks, ndim, name, safe_chunks, region, mode):
+def _determine_zarr_chunks(
+    enc_chunks, var_chunks, ndim, name, safe_chunks, region, mode
+):
     """
     Given encoding chunks (possibly None or []) and variable chunks
     (possibly None or []).
@@ -163,7 +165,9 @@ def _determine_zarr_chunks(enc_chunks, var_chunks, ndim, name, safe_chunks, regi
 
     if len(enc_chunks_tuple) != ndim:
         # throw away encoding chunks, start over
-        return _determine_zarr_chunks(None, var_chunks, ndim, name, safe_chunks, region, mode)
+        return _determine_zarr_chunks(
+            None, var_chunks, ndim, name, safe_chunks, region, mode
+        )
 
     for x in enc_chunks_tuple:
         if not isinstance(x, int):
@@ -276,7 +280,7 @@ def extract_zarr_variable_encoding(
     name=None,
     safe_chunks=True,
     region=None,
-    mode=None
+    mode=None,
 ):
     """
     Extract zarr encoding dictionary from xarray Variable
@@ -328,7 +332,7 @@ def extract_zarr_variable_encoding(
         name=name,
         safe_chunks=safe_chunks,
         region=region,
-        mode=mode
+        mode=mode,
     )
     encoding["chunks"] = chunks
     return encoding
@@ -864,7 +868,7 @@ def set_variables(self, variables, check_encoding_set, writer, unlimited_dims=No
                 raise_on_invalid=vn in check_encoding_set,
                 name=vn,
                 safe_chunks=self._safe_chunks,
-                mode=self._mode
+                mode=self._mode,
             )
 
             if name not in existing_keys:
diff --git a/xarray/tests/test_backends.py b/xarray/tests/test_backends.py
index 032a24c037c..78d50fcbdac 100644
--- a/xarray/tests/test_backends.py
+++ b/xarray/tests/test_backends.py
@@ -6157,10 +6157,7 @@ def test_zarr_safe_chunk_region(tmp_path):
     store = tmp_path / "foo.zarr"
 
     arr = xr.DataArray(
-        list(range(10)),
-        dims=["a"],
-        coords={"a": list(range(10))},
-        name="foo"
+        list(range(10)), dims=["a"], coords={"a": list(range(10))}, name="foo"
     ).chunk(a=3)
     arr.to_zarr(store, mode="w")
 
@@ -6168,18 +6165,24 @@ def test_zarr_safe_chunk_region(tmp_path):
         with pytest.raises(ValueError):
             # There are two Dask chunks on the same Zarr chunk,
             # which means that it is unsafe in any mode
-            arr.isel(a=slice(0, 3)).chunk(a=(2, 1)).to_zarr(store, region="auto", mode=mode)
+            arr.isel(a=slice(0, 3)).chunk(a=(2, 1)).to_zarr(
+                store, region="auto", mode=mode
+            )
 
         with pytest.raises(ValueError):
             # the first chunk is covering the border size, but it is not
             # completely covering the second chunk, which means that it is
             # unsafe in any mode
-            arr.isel(a=slice(1, 5)).chunk(a=(3, 1)).to_zarr(store, region="auto", mode=mode)
+            arr.isel(a=slice(1, 5)).chunk(a=(3, 1)).to_zarr(
+                store, region="auto", mode=mode
+            )
 
         with pytest.raises(ValueError):
             # The first chunk is safe but the other two chunks are overlapping with
             # the same Zarr chunk
-            arr.isel(a=slice(0, 5)).chunk(a=(3, 1, 1)).to_zarr(store, region="auto", mode=mode)
+            arr.isel(a=slice(0, 5)).chunk(a=(3, 1, 1)).to_zarr(
+                store, region="auto", mode=mode
+            )
 
         # Fully update two contiguous chunks is safe in any mode
         arr.isel(a=slice(3, 9)).to_zarr(store, region="auto", mode=mode)