expose testing functions as public API

docs/api.rst

@@ -1,5 +1,3 @@
-.. currentmodule:: xarray
-
 API reference
 =============
 This page contains a auto-generated summary of ``pint-xarray``'s API.
@@ -11,28 +9,36 @@ Dataset
    :toctree: generated/
    :template: autosummary/accessor_method.rst
 
-   Dataset.pint.quantify
-   Dataset.pint.dequantify
-   Dataset.pint.to
-   Dataset.pint.to_base_units
-   Dataset.pint.to_system
+   xarray.Dataset.pint.quantify
+   xarray.Dataset.pint.dequantify
+   xarray.Dataset.pint.to
+   xarray.Dataset.pint.to_base_units
+   xarray.Dataset.pint.to_system
 
 DataArray
 ---------
 .. autosummary::
    :toctree: generated/
    :template: autosummary/accessor_attribute.rst
 
-   DataArray.pint.magnitude
-   DataArray.pint.units
-   DataArray.pint.dimensionality
-   DataArray.pint.registry
+   xarray.DataArray.pint.magnitude
+   xarray.DataArray.pint.units
+   xarray.DataArray.pint.dimensionality
+   xarray.DataArray.pint.registry
 
 .. autosummary::
    :toctree: generated/
    :template: autosummary/accessor_method.rst
 
-   DataArray.pint.quantify
-   DataArray.pint.dequantify
-   DataArray.pint.to
-   DataArray.pint.to_base_units
+   xarray.DataArray.pint.quantify
+   xarray.DataArray.pint.dequantify
+   xarray.DataArray.pint.to
+   xarray.DataArray.pint.to_base_units
+
+Testing
+-------
+
+.. autosummary::
+   :toctree: generated/
+
+   pint_xarray.testing.assert_units_equal

pint_xarray/__init__.py

@@ -3,6 +3,7 @@
 except ImportError:
     from importlib_metadata import version
 
+from . import testing  # noqa
 from .accessors import PintDataArrayAccessor, PintDatasetAccessor  # noqa
 
 try:

pint_xarray/testing.py

@@ -0,0 +1,22 @@
+from . import conversion
+
+
+def assert_units_equal(a, b):
+    """ assert that the units of two xarray objects are equal
+
+    Raises an :py:exc:`AssertionError` if the units of both objects are not
+    equal. ``units`` attributes and attached unit objects are compared
+    separately.
+
+    Parameters
+    ----------
+    a, b : DataArray or Dataset
+        The objects to compare
+    """
+
+    __tracebackhide__ = True
+
+    assert conversion.extract_units(a) == conversion.extract_units(b)
+    assert conversion.extract_unit_attributes(a) == conversion.extract_unit_attributes(
+        b
+    )

pint_xarray/tests/test_testing.py

@@ -0,0 +1,58 @@
+import pint
+import pytest
+import xarray as xr
+
+from pint_xarray import testing
+
+unit_registry = pint.UnitRegistry(force_ndarray_like=True)
+
+
+@pytest.mark.parametrize(
+    ("a", "b", "error"),
+    (
+        pytest.param(
+            xr.DataArray(attrs={"units": "K"}),
+            xr.DataArray(attrs={"units": "K"}),
+            None,
+            id="equal attrs",
+        ),
+        pytest.param(
+            xr.DataArray(attrs={"units": "m"}),
+            xr.DataArray(attrs={"units": "K"}),
+            AssertionError,
+            id="different attrs",
+        ),
+        pytest.param(
+            xr.DataArray([10, 20] * unit_registry.K),
+            xr.DataArray([50, 80] * unit_registry.K),
+            None,
+            id="equal units",
+        ),
+        pytest.param(
+            xr.DataArray([10, 20] * unit_registry.K),
+            xr.DataArray([50, 80] * unit_registry.dimensionless),
+            AssertionError,
+            id="different units",
+        ),
+        pytest.param(
+            xr.Dataset({"a": ("x", [0, 10], {"units": "K"})}),
+            xr.Dataset({"a": ("x", [20, 40], {"units": "K"})}),
+            None,
+            id="matching variables",
+        ),
+        pytest.param(
+            xr.Dataset({"a": ("x", [0, 10], {"units": "K"})}),
+            xr.Dataset({"b": ("x", [20, 40], {"units": "K"})}),
+            AssertionError,
+            id="mismatching variables",
+        ),
+    ),
+)
+def test_assert_units_equal(a, b, error):
+    if error is not None:
+        with pytest.raises(error):
+            testing.assert_units_equal(a, b)
+
+        return
+
+    testing.assert_units_equal(a, b)

pyproject.toml

@@ -2,4 +2,5 @@
 requires = ["setuptools >= 42", "wheel", "setuptools_scm[toml] >= 3.4"]
 build-backend = "setuptools.build_meta"
 
-[tool.setuptools_scm]
+[tool.setuptools_scm]
+fallback_version = "999"