fix auto_complex for open_datatree (#10632)

* fix ``auto_complex`` for ``open_datatree``
* add TestNetCDF4DataTree test class
* add whats-new.rst entry
* prevent TestNetCDF4Data to be collected in test_backends_datatree.py
* catch ValueError for test_child_group_with_inconsistent_dimensions when run on DataTree
* fix whats-new.rst
* move internal changes to correct section

Author: kmuehlbauer

doc/whats-new.rst

@@ -24,6 +24,8 @@ Deprecations
 
 Bug fixes
 ~~~~~~~~~
+- Fix distribution of ``auto_complex`` keyword argument for open_datatree (:issue:`10631`, :pull:`10632`).
+  By `Kai Mühlbauer <https://github.com/kmuehlbauer>`_.
 
 
 Documentation
@@ -32,6 +34,9 @@ Documentation
 
 Internal Changes
 ~~~~~~~~~~~~~~~~
+- Run ``TestNetCDF4Data`` as ``TestNetCDF4DataTree`` through ``open_datatree`` (:pull:`10632`).
+  By `Kai Mühlbauer <https://github.com/kmuehlbauer>`_.
+
 
 .. _whats-new.2025.08.0:
 

xarray/backends/netCDF4_.py

@@ -730,6 +730,7 @@ def open_datatree(
             clobber=clobber,
             diskless=diskless,
             persist=persist,
+            auto_complex=auto_complex,
             lock=lock,
             autoclose=autoclose,
             **kwargs,
@@ -769,6 +770,7 @@ def open_groups_as_dict(
             clobber=clobber,
             diskless=diskless,
             persist=persist,
+            auto_complex=auto_complex,
             lock=lock,
             autoclose=autoclose,
         )

xarray/tests/test_backends_datatree.py

@@ -23,6 +23,7 @@
     requires_pydap,
     requires_zarr,
 )
+from xarray.tests.test_backends import TestNetCDF4Data as _TestNetCDF4Data
 
 if TYPE_CHECKING:
     from xarray.core.datatree_io import T_DataTreeNetcdfEngine
@@ -31,6 +32,19 @@
     import netCDF4 as nc4
 
 
+class TestNetCDF4DataTree(_TestNetCDF4Data):
+    @contextlib.contextmanager
+    def open(self, path, **kwargs):
+        with open_datatree(path, engine=self.engine, **kwargs) as ds:
+            yield ds.to_dataset()
+
+    def test_child_group_with_inconsistent_dimensions(self) -> None:
+        with pytest.raises(
+            ValueError, match=r"group '/child' is not aligned with its parents"
+        ):
+            super().test_child_group_with_inconsistent_dimensions()
+
+
 def diff_chunks(
     comparison: dict[tuple[str, Hashable], bool], tree1: DataTree, tree2: DataTree
 ) -> str: