fixes for the pint tests

ci/install-upstream-wheels.sh

@@ -48,6 +48,8 @@ python -m pip install \
     --pre \
     --upgrade \
     pyarrow
+# manually install `pint` to pull in new dependencies
+python -m pip install --upgrade pint
 python -m pip install \
     --no-deps \
     --upgrade \

xarray/tests/test_units.py

@@ -34,6 +34,7 @@
 # always be treated like ndarrays
 unit_registry = pint.UnitRegistry(force_ndarray_like=True)
 Quantity = unit_registry.Quantity
+no_unit_values = ("none", None)
 
 
 pytestmark = [
@@ -91,17 +92,13 @@ def array_strip_units(array):
 
 
 def array_attach_units(data, unit):
-    if isinstance(data, Quantity):
+    if isinstance(data, Quantity) and data.units != unit:
         raise ValueError(f"cannot attach unit {unit} to quantity {data}")
 
-    try:
-        quantity = data * unit
-    except np.core._exceptions.UFuncTypeError:
-        if isinstance(unit, unit_registry.Unit):
-            raise
-
-        quantity = data
+    if unit in no_unit_values or (isinstance(unit, int) and unit == 1):
+        return data
 
+    quantity = unit_registry.Quantity(data, unit)
     return quantity