issues: 559873728

https://dev.azure.com/xarray/xarray/_build/results?buildId=2116&view=logs&jobId=2280efed-fda1-53bd-9213-1fa8ec9b4fa8&j=2280efed-fda1-53bd-9213-1fa8ec9b4fa8&t=175181ee-1928-5a6b-f537-168f7a8b7c2d

46 failed tests but they all seem to result from the same TypeError

``` =================================== FAILURES =================================== __ test_sel_date_scalar_nearest[365_day-sel_kwargs0] ___

da = <xarray.DataArray (time: 4)> 0002-02-01 00:00:00], dtype='object') sel_kwargs = {'method': 'nearest'}

@requires_cftime
@pytest.mark.parametrize(
    "sel_kwargs",
    [{"method": "nearest"}, {"method": "nearest", "tolerance": timedelta(days=70)}],
)
def test_sel_date_scalar_nearest(da, date_type, index, sel_kwargs):
    expected = xr.DataArray(2).assign_coords(time=index[1])

  result = da.sel(time=date_type(1, 4, 1), **sel_kwargs)

xarray/tests/test_cftimeindex.py:460:

xarray/core/dataarray.py:1056: in sel ds = self._to_temp_dataset().sel( xarray/core/dataset.py:2056: in sel pos_indexers, new_indexes = remap_label_indexers( xarray/core/coordinates.py:391: in remap_label_indexers pos_indexers, new_indexes = indexing.remap_label_indexers( xarray/core/indexing.py:270: in remap_label_indexers idxr, new_idx = convert_label_indexer(index, label, dim, method, tolerance) xarray/core/indexing.py:189: in convert_label_indexer indexer = index.get_loc( xarray/coding/cftimeindex.py:334: in get_loc return pd.Index.get_loc(self, key, method=method, tolerance=tolerance) /usr/share/miniconda/envs/xarray-tests/lib/python3.8/site-packages/pandas/core/indexes/base.py:2899: in get_loc indexer = self.get_indexer([key], method=method, tolerance=tolerance) /usr/share/miniconda/envs/xarray-tests/lib/python3.8/site-packages/pandas/core/indexes/base.py:2992: in get_indexer indexer = self._get_nearest_indexer(target, limit, tolerance) /usr/share/miniconda/envs/xarray-tests/lib/python3.8/site-packages/pandas/core/indexes/base.py:3076: in _get_nearest_indexer left_distances = np.abs(self[left_indexer] - target) xarray/coding/cftimeindex.py:444: in sub return CFTimeIndex(np.array(self) - other) xarray/coding/cftimeindex.py:248: in new assert_all_valid_date_type(data)

data = TimedeltaIndex(['-59 days'], dtype='timedelta64[ns]', freq=None)

def assert_all_valid_date_type(data):
    import cftime

    if len(data) > 0:
        sample = data[0]
        date_type = type(sample)
        if not isinstance(sample, cftime.datetime):

          raise TypeError(
                "CFTimeIndex requires cftime.datetime "
                "objects. Got object of {}.".format(date_type)
            )

E TypeError: CFTimeIndex requires cftime.datetime objects. Got object of <class 'pandas._libs.tslibs.timedeltas.Timedelta'>.

xarray/coding/cftimeindex.py:206: TypeError ```