Some aggregate operations using the array API fail

[tomwhite]

What happened?

Here are some tests demonstrating the problem 9d6269d:

FAILED xarray/tests/test_array_api.py::test_aggregation[max] - assert False
FAILED xarray/tests/test_array_api.py::test_aggregation[min] - assert False
FAILED xarray/tests/test_array_api.py::test_aggregation[mean] - assert False
FAILED xarray/tests/test_array_api.py::test_aggregation[prod] - assert False
FAILED xarray/tests/test_array_api.py::test_aggregation[std] - assert False
FAILED xarray/tests/test_array_api.py::test_aggregation[var] - assert False
FAILED xarray/tests/test_array_api.py::test_aggregation_skipna[std] - TypeError: std() got an unexpected keyword argument 'ddof'
FAILED xarray/tests/test_array_api.py::test_aggregation_skipna[var] - TypeError: var() got an unexpected keyword argument 'ddof'

What did you expect to happen?

No response

Minimal Complete Verifiable Example

No response

MVCE confirmation

• Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• Complete example — the example is self-contained, including all data and the text of any traceback.
• Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
• New issue — a search of GitHub Issues suggests this is not a duplicate.

Relevant log output

No response

Anything else we need to know?

No response

Environment

INSTALLED VERSIONS

commit: 9d6269d
python: 3.8.13 (default, Mar 28 2022, 06:16:26)
[Clang 12.0.0 ]
python-bits: 64
OS: Darwin
OS-release: 21.6.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: en_GB.UTF-8
LOCALE: ('en_GB', 'UTF-8')
libhdf5: None
libnetcdf: None

xarray: 2022.6.1.dev63+ge6791852a
pandas: 1.5.0
numpy: 1.23.3
scipy: None
netCDF4: None
pydap: None
h5netcdf: None
h5py: None
Nio: None
zarr: None
cftime: None
nc_time_axis: None
PseudoNetCDF: None
rasterio: None
cfgrib: None
iris: None
bottleneck: None
dask: None
distributed: None
matplotlib: None
cartopy: None
seaborn: None
numbagg: None
fsspec: None
cupy: None
pint: None
sparse: None
flox: None
numpy_groupies: None
setuptools: 63.4.1
pip: 22.1.2
conda: None
pytest: 7.1.3
IPython: None
sphinx: None