Test for warnings fail when using old version of pytest

[shoyer]

Some of our tests for warnings currently fail when run using an old version of pytest. The problem appears to be that we rely on pytest.warns() accepting subclasses rather exact matches.

This was fixed upstream in pytest (pytest-dev/pytest#2166), but we still should specify the more specific warning types in xarray.

=================================== FAILURES ===================================
_________________ TestEncodeCFVariable.test_missing_fillvalue __________________

self = <xarray.tests.test_conventions.TestEncodeCFVariable testMethod=test_missing_fillvalue>

    def test_missing_fillvalue(self):
        v = Variable(['x'], np.array([np.nan, 1, 2, 3]))
        v.encoding = {'dtype': 'int16'}
        with pytest.warns(Warning, match='floating point data as an integer'):
>           conventions.encode_cf_variable(v)
E           Failed: DID NOT WARN

tests/test_conventions.py:89: Failed

________________________________ TestAlias.test ________________________________

self = <xarray.tests.test_utils.TestAlias testMethod=test>

    def test(self):
        def new_method():
            pass
        old_method = utils.alias(new_method, 'old_method')
        assert 'deprecated' in old_method.__doc__
        with pytest.warns(Warning, match='deprecated'):
>           old_method()
E           Failed: DID NOT WARN

tests/test_utils.py:28: Failed

___________________ TestIndexVariable.test_coordinate_alias ____________________

self = <xarray.tests.test_variable.TestIndexVariable testMethod=test_coordinate_alias>

    def test_coordinate_alias(self):
        with pytest.warns(Warning, match='deprecated'):
>           x = Coordinate('x', [1, 2, 3])
E           Failed: DID NOT WARN

tests/test_variable.py:1752: Failed
__________________________ TestAccessor.test_register __________________________

self = <xarray.tests.test_extensions.TestAccessor testMethod=test_register>

    def test_register(self):
    
        @xr.register_dataset_accessor('demo')
        @xr.register_dataarray_accessor('demo')
        class DemoAccessor(object):
            """Demo accessor."""
    
            def __init__(self, xarray_obj):
                self._obj = xarray_obj
    
            @property
            def foo(self):
                return 'bar'
    
        ds = xr.Dataset()
        assert ds.demo.foo == 'bar'
    
        da = xr.DataArray(0)
        assert da.demo.foo == 'bar'
    
        # accessor is cached
        assert ds.demo is ds.demo
    
        # check descriptor
        assert ds.demo.__doc__ == "Demo accessor."
        assert xr.Dataset.demo.__doc__ == "Demo accessor."
        assert isinstance(ds.demo, DemoAccessor)
        assert xr.Dataset.demo is DemoAccessor
    
        # ensure we can remove it
        del xr.Dataset.demo
        assert not hasattr(xr.Dataset, 'demo')
    
        with pytest.warns(Warning, match='overriding a preexisting attribute'):
            @xr.register_dataarray_accessor('demo')
>           class Foo(object):
E           Failed: DID NOT WARN

tests/test_extensions.py:60: Failed

[max-sixty]

Can we close this given the updated pytest has been out for two years?

(though in general ofc we should test for the more specific warning)

[shoyer]

agreed