temporarily remove placeholder functions (#29)

* remove to_base_units, plus_minus and to_system

* remove placeholder tests and test groups

pint_xarray/accessors.py

@@ -4,12 +4,7 @@
 import pint
 from pint.quantity import Quantity
 from pint.unit import Unit
-from xarray import (
-    DataArray,
-    Dataset,
-    register_dataarray_accessor,
-    register_dataset_accessor,
-)
+from xarray import DataArray, register_dataarray_accessor, register_dataset_accessor
 from xarray.core.npcompat import IS_NEP18_ACTIVE
 
 from . import conversion
@@ -375,27 +370,6 @@ def to(self, units=None, **unit_kwargs):
 
         return conversion.convert_units(self.da, units)
 
-    def to_base_units(self):
-        quantity = self.da.data.to_base_units()
-        return DataArray(
-            dim=self.da.dims,
-            data=quantity,
-            coords=self.da.coords,
-            attrs=self.da.attrs,
-            encoding=self.da.encoding,
-        )
-
-    # TODO integrate with the uncertainties package here...?
-    def plus_minus(self, value, error, relative=False):
-        quantity = self.da.data.plus_minus(value, error, relative)
-        return DataArray(
-            dim=self.da.dims,
-            data=quantity,
-            coords=self.da.coords,
-            attrs=self.da.attrs,
-            encoding=self.da.encoding,
-        )
-
     def sel(
         self, indexers=None, method=None, tolerance=None, drop=False, **indexers_kwargs
     ):
@@ -630,14 +604,6 @@ def to(self, units=None, **unit_kwargs):
 
         return conversion.convert_units(self.ds, units)
 
-    def to_base_units(self):
-        base_vars = {name: da.pint.to_base_units() for name, da in self.ds.items()}
-        return Dataset(base_vars, coords=self.ds.coords, attrs=self.ds.attrs)
-
-    # TODO unsure if the upstream capability exists in pint for this yet.
-    def to_system(self, system):
-        raise NotImplementedError
-
     def sel(
         self, indexers=None, method=None, tolerance=None, drop=False, **indexers_kwargs
     ):

pint_xarray/tests/test_accessors.py

@@ -147,24 +147,6 @@ def example_quantity_ds():
     return ds
 
 
-@pytest.mark.skip(reason="Not yet implemented")
-class TestPropertiesDataArray:
-    def test_units(self):
-        ...
-
-
-@pytest.mark.skip(reason="Not yet implemented")
-class TestConversionDataArray:
-    def test_units(self):
-        ...
-
-
-@pytest.mark.skip(reason="Not yet implemented")
-class TestUncertainties:
-    def test_units(self):
-        ...
-
-
 class TestQuantifyDataSet:
     def test_attach_units_from_str(self, example_unitless_ds):
         orig = example_unitless_ds
@@ -242,8 +224,3 @@ def test_roundtrip_data(self, example_unitless_ds):
 
         result = quantified.pint.dequantify().pint.quantify()
         assert_equal(quantified, result)
-
-
-@pytest.mark.skip(reason="Not yet implemented")
-class TestIndexing:
-    ...