issue_comments: 774101639

Thanks! That drove me nuts but I finally figured out the problem:

https://github.com/pydata/xarray/blob/5735e163bea43ec9bc3c2e640fbf25a1d4a9d0c0/xarray/tests/test_units.py#L29

promotes the warning to an error so diff_array_repr fails (because the units are stripped...) and that is what we see. That also fails on master - run the following in with pytest:

```python import pint import pytest import xarray as xr

pytestmark = [ pytest.mark.filterwarnings("error::pint.UnitStrippedWarning"), ]

unit_registry = pint.UnitRegistry(force_ndarray=True)

def test_y():

data_array1 = xr.DataArray(data=1 * unit_registry.m)
data_array2 = xr.DataArray(data=2 * unit_registry.m)

xr.testing.assert_allclose(data_array1, data_array2)

```

@keewis do you have an idea how to fix this? One idea is to supress warnings in diff_array_repr and diff_dataset_repr. Do we need to strip the units before sending them to these functions?