fixing behaviour for group parameter in open_datatree

xarray/tests/test_backends_datatree.py

@@ -240,6 +240,38 @@ def test_open_groups_to_dict(self, tmpdir) -> None:
         for ds in aligned_dict_of_datasets.values():
             ds.close()
 
+    def test_open_datatree_specific_group(self, tmpdir, simple_datatree) -> None:
+        """Test opening a specific group within a NetCDF file using `open_datatree`."""
+        # Open the specific group '/Group1/subgroup1' and check if it loads correctly
+        filepath = tmpdir / "test.nc"
+        group = "/set1"
+        original_dt = simple_datatree
+        original_dt.to_netcdf(filepath)
+
+        with open_datatree(filepath, group=group, engine=self.engine) as subgroup_tree:
+            # Check that the subtree is not None
+            assert subgroup_tree is not None
+            # Check the expected number of children within node
+            assert list(subgroup_tree.children) == list(original_dt[group].children)
+            # Check the dimensions of the group '/set1'
+            assert len(subgroup_tree.dataset.dims) == len(original_dt[group].dataset.dims)
+            # Check if the variables in this "set1" group are correctly read
+            assert list(subgroup_tree.dataset.data_vars) == list(original_dt[group].dataset.data_vars)
+            # Check the values of the variables 'a' and 'b'
+            assert subgroup_tree.dataset["a"].values == original_dt[group].dataset["a"].values
+            assert subgroup_tree.dataset["b"].values == original_dt[group].dataset["b"].values
+
+    def test_open_datatree_nonexistent_group(self, tmpdir, simple_datatree) -> None:
+        """Test `open_datatree` behavior when attempting to open a non-existent group."""
+        filepath = tmpdir / "test.nc"
+        original_dt = simple_datatree
+        original_dt.to_netcdf(filepath, engine=self.engine)
+
+        # Attempt to open a non-existent group, which should raise a ValueError
+        with pytest.raises(OSError, match="Group '/nonexistent_group' not found"):
+            open_datatree(filepath, group="/nonexistent_group", engine=self.engine)
+
+
 
 @requires_h5netcdf
 class TestH5NetCDFDatatreeIO(DatatreeIOBase):
@@ -382,3 +414,23 @@ def test_open_groups(self, unaligned_datatree_zarr) -> None:
 
         for ds in unaligned_dict_of_datasets.values():
             ds.close()
+
+    def test_open_datatree_specific_group(self, tmpdir, simple_datatree) -> None:
+        """Test opening a specific group within a Zarr store using `open_datatree`."""
+        filepath = tmpdir / "test.zarr"
+        group = "/set2"
+        original_dt = simple_datatree
+        original_dt.to_zarr(filepath)
+
+        with open_datatree(filepath, group=group, engine=self.engine) as subgroup_tree:
+            # Check that the subtree is not None
+            assert subgroup_tree is not None
+            # Check the expected number of children within node
+            assert list(subgroup_tree.children) == list(original_dt[group].children)
+            # Check the dimensions of the group '/set2'
+            assert len(subgroup_tree.dataset.dims) == len(original_dt[group].dataset.dims)
+            # Check if the variables in this "set2" group are correctly read
+            assert list(subgroup_tree.dataset.data_vars) == list(original_dt[group].dataset.data_vars)
+            # Check the values of the variables 'a' and 'b'
+            assert_equal(subgroup_tree.dataset["a"], original_dt[group].dataset["a"])
+            assert_equal(subgroup_tree.dataset["b"], original_dt[group].dataset["b"])