2nd change after review

Author: makbigc

doc/source/whatsnew/v0.24.0.txt

@@ -858,6 +858,8 @@ update the ``ExtensionDtype._metadata`` tuple to match the signature of your
 - :meth:`DataFrame.stack` no longer converts to object dtype for DataFrames where each column has the same extension dtype. The output Series will have the same dtype as the columns (:issue:`23077`).
 - :meth:`Series.unstack` and :meth:`DataFrame.unstack` no longer convert extension arrays to object-dtype ndarrays. Each column in the output ``DataFrame`` will now have the same dtype as the input (:issue:`23077`).
 - Bug when grouping :meth:`Dataframe.groupby()` and aggregating on ``ExtensionArray`` it was not returning the actual ``ExtensionArray`` dtype (:issue:`23227`).
+- :meth:`Series.unstack` no longer converts extension arrays to object-dtype ndarrays. The output ``DataFrame`` will now have the same dtype as the input. This changes behavior for Categorical and Sparse data (:issue:`23077`).
+- Bug in :func:`pandas.merge` when merging on an Integer extension array (:issue:`23020`)
 
 .. _whatsnew_0240.api.incompatibilities:
 
@@ -1360,12 +1362,6 @@ Sparse
 - Bug in unary inversion operator (``~``) on a ``SparseSeries`` with boolean values. The performance of this has also been improved (:issue:`22835`)
 - Bug in :meth:`SparseArary.unique` not returning the unique values (:issue:`19595`)
 
-IntegerArray
-^^^^^^^^^^^^
-
-- Bug in :func:`pandas.merge` when merging on an Integer extension array (:issue:`23020`)
-
-
 Build Changes
 ^^^^^^^^^^^^^
 

pandas/tests/extension/base/reshaping.py

@@ -173,6 +173,20 @@ def test_merge(self, data, na_value):
                  dtype=data.dtype)})
         self.assert_frame_equal(res, exp[['ext', 'int1', 'key', 'int2']])
 
+        # GH  23020
+        df1 = pd.DataFrame({'ext': data[:3],
+                            'key': pd.Series([1, 2, np.nan], dtype='Int64')})
+
+        res = pd.merge(df1, df1, on='key')
+
+        exp = pd.DataFrame(
+            {'key': pd.Series([1, 2, np.nan], dtype='Int64'),
+             'ext_x': data._from_sequence(data[:3], dtype=data.dtype),
+             'ext_y': data._from_sequence(data[:3], dtype=data.dtype)})
+
+        self.assert_frame_equal(res, exp[['ext_x', 'key', 'ext_y']],
+                                check_dtype=True)
+
     @pytest.mark.parametrize("columns", [
         ["A", "B"],
         pd.MultiIndex.from_tuples([('A', 'a'), ('A', 'b')],
@@ -237,11 +251,3 @@ def test_unstack(self, data, index, obj):
             result = result.astype(object)
 
             self.assert_frame_equal(result, expected)
-
-    def test_merge_on_int_array(self, df_merge_on_int_array):
-        # GH  23020
-        result = pd.merge(df_merge_on_int_array, df_merge_on_int_array, on='A')
-        expected = pd.DataFrame({'A': pd.Series([1, 2, np.nan], dtype='Int64'),
-                                 'B_x': 1,
-                                 'B_y': 1})
-        self.assert_frame_equal(result, expected, check_dtype=True)

pandas/tests/extension/conftest.py

@@ -1,5 +1,3 @@
-import pandas as pd
-import numpy as np
 import operator
 
 import pytest
@@ -106,9 +104,3 @@ def data_for_grouping():
 def box_in_series(request):
     """Whether to box the data in a Series"""
     return request.param
-
-
-@pytest.fixture
-def df_merge_on_int_array():
-    return pd.DataFrame({'A': pd.Series([1, 2, np.nan], dtype='Int64'),
-                         'B': 1})