TST: enable 2D tests for MaskedArrays, fix+test shift (#61826)

Author: jbrockmendel

pandas/core/arrays/masked.py

@@ -59,6 +59,7 @@
     masked_reductions,
 )
 from pandas.core.array_algos.quantile import quantile_with_mask
+from pandas.core.array_algos.transforms import shift
 from pandas.core.arraylike import OpsMixin
 from pandas.core.arrays._utils import to_numpy_dtype_inference
 from pandas.core.arrays.base import ExtensionArray
@@ -361,6 +362,17 @@ def ravel(self, *args, **kwargs) -> Self:
         mask = self._mask.ravel(*args, **kwargs)
         return type(self)(data, mask)
 
+    def shift(self, periods: int = 1, fill_value=None) -> Self:
+        # NB: shift is always along axis=0
+        axis = 0
+        if fill_value is None:
+            new_data = shift(self._data, periods, axis, 0)
+            new_mask = shift(self._mask, periods, axis, True)
+        else:
+            new_data = shift(self._data, periods, axis, fill_value)
+            new_mask = shift(self._mask, periods, axis, False)
+        return type(self)(new_data, new_mask)
+
     @property
     def T(self) -> Self:
         return self._simple_new(self._data.T, self._mask.T)

pandas/tests/extension/base/dim2.py

@@ -32,6 +32,16 @@ def skip_if_doesnt_support_2d(self, dtype, request):
                 # TODO: is there a less hacky way of checking this?
                 pytest.skip(f"{dtype} does not support 2D.")
 
+    def test_shift_2d(self, data):
+        arr2d = data.repeat(2).reshape(-1, 2)
+
+        for n in [1, -2]:
+            for fill_value in [None, data[0]]:
+                result = arr2d.shift(n, fill_value=fill_value)
+                expected_col = data.shift(n, fill_value=fill_value)
+                tm.assert_extension_array_equal(result[:, 0], expected_col)
+                tm.assert_extension_array_equal(result[:, 1], expected_col)
+
     def test_transpose(self, data):
         arr2d = data.repeat(2).reshape(-1, 2)
         shape = arr2d.shape

pandas/tests/extension/test_masked.py

@@ -168,6 +168,13 @@ def data_for_grouping(dtype):
 
 
 class TestMaskedArrays(base.ExtensionTests):
+    @pytest.fixture(autouse=True)
+    def skip_if_doesnt_support_2d(self, dtype, request):
+        # Override the fixture so that we run these tests.
+        assert not dtype._supports_2d
+        # If dtype._supports_2d is ever changed to True, then this fixture
+        #  override becomes unnecessary.
+
     @pytest.mark.parametrize("na_action", [None, "ignore"])
     def test_map(self, data_missing, na_action):
         result = data_missing.map(lambda x: x, na_action=na_action)
@@ -402,7 +409,3 @@ def check_accumulate(self, ser: pd.Series, op_name: str, skipna: bool):
 
         else:
             raise NotImplementedError(f"{op_name} not supported")
-
-
-class Test2DCompat(base.Dim2CompatTests):
-    pass