support datatree in assert_allclose

doc/whats-new.rst

@@ -19,6 +19,8 @@ New Features
   By `Stephan Hoyer <https://github.com/shoyer>`_.
 - The ``h5netcdf`` engine has support for pseudo ``NETCDF4_CLASSIC`` files, meaning variables and attributes are cast to supported types. Note that the saved files won't be recognized as genuine ``NETCDF4_CLASSIC`` files until ``h5netcdf`` adds support with version 1.7.0. (:issue:`10676`, :pull:`10686`).
   By `David Huard <https://github.com/huard>`_.
+- Support comparing :py:class:`DataTree` objects with :py:func:`testing.assert_allclose` (:pull:`10887`).
+  By `Justus Magin <https://github.com/keewis>`_.
 
 Breaking Changes
 ~~~~~~~~~~~~~~~~

xarray/core/dataset.py

@@ -1506,13 +1506,18 @@ def __delitem__(self, key: Hashable) -> None:
     # https://github.com/python/mypy/issues/4266
     __hash__ = None  # type: ignore[assignment]
 
-    def _all_compat(self, other: Self, compat_str: str) -> bool:
+    def _all_compat(
+        self, other: Self, compat: str | Callable[[Variable, Variable], bool]
+    ) -> bool:
         """Helper function for equals and identical"""
 
-        # some stores (e.g., scipy) do not seem to preserve order, so don't
-        # require matching order for equality
-        def compat(x: Variable, y: Variable) -> bool:
-            return getattr(x, compat_str)(y)
+        if not callable(compat):
+            compat_str = compat
+
+            # some stores (e.g., scipy) do not seem to preserve order, so don't
+            # require matching order for equality
+            def compat(x: Variable, y: Variable) -> bool:
+                return getattr(x, compat_str)(y)
 
         return self._coord_names == other._coord_names and utils.dict_equiv(
             self._variables, other._variables, compat=compat

xarray/testing/assertions.py

@@ -239,6 +239,11 @@ def compat_variable(a, b):
         b = getattr(b, "variable", b)
         return a.dims == b.dims and (a._data is b._data or equiv(a.data, b.data))
 
+    def compat_node(a, b):
+        return a.ds._coord_names == b.ds._coord_names and utils.dict_equiv(
+            a.variables, b.variables, compat=compat_variable
+        )
+
     if isinstance(a, Variable):
         allclose = compat_variable(a, b)
         assert allclose, formatting.diff_array_repr(a, b, compat=equiv)
@@ -255,6 +260,11 @@ def compat_variable(a, b):
     elif isinstance(a, Coordinates):
         allclose = utils.dict_equiv(a.variables, b.variables, compat=compat_variable)
         assert allclose, formatting.diff_coords_repr(a, b, compat=equiv)
+    elif isinstance(a, DataTree):
+        allclose = utils.dict_equiv(
+            dict(a.subtree_with_keys), dict(b.subtree_with_keys), compat=compat_node
+        )
+        assert allclose, formatting.diff_datatree_repr(a, b, compat=equiv)
     else:
         raise TypeError(f"{type(a)} not supported by assertion comparison")
 

xarray/tests/test_assertions.py

@@ -62,6 +62,19 @@ def test_allclose_regression() -> None:
             xr.Coordinates({"x": [0, 3]}),
             id="Coordinates",
         ),
+        pytest.param(
+            xr.DataTree.from_dict(
+                {
+                    "/b": xr.Dataset({"a": ("x", [1e-17, 2]), "b": ("y", [-2e-18, 2])}),
+                }
+            ),
+            xr.DataTree.from_dict(
+                {
+                    "/b": xr.Dataset({"a": ("x", [0, 2]), "b": ("y", [0, 1])}),
+                }
+            ),
+            id="DataTree",
+        ),
     ),
 )
 def test_assert_allclose(obj1, obj2) -> None: