Add argument check_dims to assert_allclose to allow transposed inputs (#5733) (#8991)

* Add argument check_dims to assert_allclose to allow transposed inputs

* Update whats-new.rst

* Add `check_dims` argument to assert_equal and assert_identical + tests

* Assert that dimensions match before transposing or comparing values

* Add docstring for check_dims to assert_equal and assert_identical

* Update doc/whats-new.rst

Co-authored-by: Tom Nicholas <tom@cworthy.org>

* Undo fat finger

Co-authored-by: Tom Nicholas <tom@cworthy.org>

* Add attribution to whats-new.rst

* Replace check_dims with bool argument check_dim_order, rename align_dims to maybe_transpose_dims

* Remove left-over half-made test

* Remove check_dim_order argument from assert_identical

* assert_allclose/equal: emit full diff if dimensions don't match

* Rename check_dim_order test, test Dataset with different dim orders

* Update whats-new.rst

* Hide maybe_transpose_dims from Pytest traceback

Co-authored-by: Maximilian Roos <5635139+max-sixty@users.noreply.github.com>

* Ignore mypy error due to missing functools.partial.__name__

---------

Co-authored-by: Tom Nicholas <tom@cworthy.org>
Co-authored-by: Maximilian Roos <5635139+max-sixty@users.noreply.github.com>

Author: 3 people

doc/whats-new.rst

@@ -29,6 +29,8 @@ New Features
   for example, will retain the object.  However, one cannot do operations that are not possible on the `ExtensionArray`
   then, such as broadcasting.
   By `Ilan Gold <https://github.com/ilan-gold>`_.
+- :py:func:`testing.assert_allclose`/:py:func:`testing.assert_equal` now accept a new argument `check_dims="transpose"`, controlling whether a transposed array is considered equal. (:issue:`5733`, :pull:`8991`)
+  By `Ignacio Martinez Vazquez <https://github.com/ignamv>`_.
 - Added the option to avoid automatically creating 1D pandas indexes in :py:meth:`Dataset.expand_dims()`, by passing the new kwarg
   `create_index=False`. (:pull:`8960`)
   By `Tom Nicholas <https://github.com/TomNicholas>`_.

xarray/testing/assertions.py

@@ -95,6 +95,18 @@ def assert_isomorphic(a: DataTree, b: DataTree, from_root: bool = False):
         raise TypeError(f"{type(a)} not of type DataTree")
 
 
+def maybe_transpose_dims(a, b, check_dim_order: bool):
+    """Helper for assert_equal/allclose/identical"""
+    __tracebackhide__ = True
+    if not isinstance(a, (Variable, DataArray, Dataset)):
+        return b
+    if not check_dim_order and set(a.dims) == set(b.dims):
+        # Ensure transpose won't fail if a dimension is missing
+        # If this is the case, the difference will be caught by the caller
+        return b.transpose(*a.dims)
+    return b
+
+
 @overload
 def assert_equal(a, b): ...
 
@@ -104,7 +116,7 @@ def assert_equal(a: DataTree, b: DataTree, from_root: bool = True): ...
 
 
 @ensure_warnings
-def assert_equal(a, b, from_root=True):
+def assert_equal(a, b, from_root=True, check_dim_order: bool = True):
     """Like :py:func:`numpy.testing.assert_array_equal`, but for xarray
     objects.
 
@@ -127,6 +139,8 @@ def assert_equal(a, b, from_root=True):
         Only used when comparing DataTree objects. Indicates whether or not to
         first traverse to the root of the trees before checking for isomorphism.
         If a & b have no parents then this has no effect.
+    check_dim_order : bool, optional, default is True
+        Whether dimensions must be in the same order.
 
     See Also
     --------
@@ -137,6 +151,7 @@ def assert_equal(a, b, from_root=True):
     assert (
         type(a) == type(b) or isinstance(a, Coordinates) and isinstance(b, Coordinates)
     )
+    b = maybe_transpose_dims(a, b, check_dim_order)
     if isinstance(a, (Variable, DataArray)):
         assert a.equals(b), formatting.diff_array_repr(a, b, "equals")
     elif isinstance(a, Dataset):
@@ -182,6 +197,8 @@ def assert_identical(a, b, from_root=True):
         Only used when comparing DataTree objects. Indicates whether or not to
         first traverse to the root of the trees before checking for isomorphism.
         If a & b have no parents then this has no effect.
+    check_dim_order : bool, optional, default is True
+        Whether dimensions must be in the same order.
 
     See Also
     --------
@@ -213,7 +230,9 @@ def assert_identical(a, b, from_root=True):
 
 
 @ensure_warnings
-def assert_allclose(a, b, rtol=1e-05, atol=1e-08, decode_bytes=True):
+def assert_allclose(
+    a, b, rtol=1e-05, atol=1e-08, decode_bytes=True, check_dim_order: bool = True
+):
     """Like :py:func:`numpy.testing.assert_allclose`, but for xarray objects.
 
     Raises an AssertionError if two objects are not equal up to desired
@@ -233,23 +252,25 @@ def assert_allclose(a, b, rtol=1e-05, atol=1e-08, decode_bytes=True):
         Whether byte dtypes should be decoded to strings as UTF-8 or not.
         This is useful for testing serialization methods on Python 3 that
         return saved strings as bytes.
+    check_dim_order : bool, optional, default is True
+        Whether dimensions must be in the same order.
 
     See Also
     --------
     assert_identical, assert_equal, numpy.testing.assert_allclose
     """
     __tracebackhide__ = True
     assert type(a) == type(b)
+    b = maybe_transpose_dims(a, b, check_dim_order)
 
     equiv = functools.partial(
         _data_allclose_or_equiv, rtol=rtol, atol=atol, decode_bytes=decode_bytes
     )
-    equiv.__name__ = "allclose"
+    equiv.__name__ = "allclose"  # type: ignore[attr-defined]
 
     def compat_variable(a, b):
         a = getattr(a, "variable", a)
         b = getattr(b, "variable", b)
-
         return a.dims == b.dims and (a._data is b._data or equiv(a.data, b.data))
 
     if isinstance(a, Variable):

xarray/tests/test_assertions.py

@@ -57,6 +57,25 @@ def test_allclose_regression() -> None:
 def test_assert_allclose(obj1, obj2) -> None:
     with pytest.raises(AssertionError):
         xr.testing.assert_allclose(obj1, obj2)
+    with pytest.raises(AssertionError):
+        xr.testing.assert_allclose(obj1, obj2, check_dim_order=False)
+
+
+@pytest.mark.parametrize("func", ["assert_equal", "assert_allclose"])
+def test_assert_allclose_equal_transpose(func) -> None:
+    """Transposed DataArray raises assertion unless check_dim_order=False."""
+    obj1 = xr.DataArray([[0, 1, 2], [2, 3, 4]], dims=["a", "b"])
+    obj2 = xr.DataArray([[0, 2], [1, 3], [2, 4]], dims=["b", "a"])
+    with pytest.raises(AssertionError):
+        getattr(xr.testing, func)(obj1, obj2)
+    getattr(xr.testing, func)(obj1, obj2, check_dim_order=False)
+    ds1 = obj1.to_dataset(name="varname")
+    ds1["var2"] = obj1
+    ds2 = obj1.to_dataset(name="varname")
+    ds2["var2"] = obj1.transpose()
+    with pytest.raises(AssertionError):
+        getattr(xr.testing, func)(ds1, ds2)
+    getattr(xr.testing, func)(ds1, ds2, check_dim_order=False)
 
 
 @pytest.mark.filterwarnings("error")