test that auto append fails

xarray/tests/test_backends.py

@@ -5350,6 +5350,40 @@ def test_zarr_region_index_write(self, tmp_path):
                 assert "x" not in written_variables
                 assert "y" not in written_variables
 
+    def test_zarr_region_append(self, tmp_path):
+        x = np.arange(0, 50, 10)
+        y = np.arange(0, 20, 2)
+        data = np.ones((5, 10))
+        ds = xr.Dataset(
+            {
+                "test": xr.DataArray(
+                    data,
+                    dims=("x", "y"),
+                    coords={"x": x, "y": y},
+                )
+            }
+        )
+        ds.to_zarr(tmp_path / "test.zarr")
+
+        x_new = np.arange(40, 70, 10)
+        data_new = np.ones((3, 10))
+        ds_new = xr.Dataset(
+            {
+                "test": xr.DataArray(
+                    data_new,
+                    dims=("x", "y"),
+                    coords={"x": x_new, "y": y},
+                )
+            }
+        )
+
+        # Don't allow auto region detection in append mode due to complexities in
+        # implementing the overlap logic and lack of safety with parallel writes
+        with pytest.raises(ValueError):
+            ds_new.to_zarr(
+                tmp_path / "test.zarr", mode="a", append_dim="x", region="auto"
+            )
+
 
 @requires_zarr
 def test_zarr_region_transpose(tmp_path):