Add test and fix whatsnew entry

Author: ABizzinotto

doc/source/whatsnew/v2.1.2.rst

@@ -30,7 +30,7 @@ Bug fixes
 - Fixed bug in :meth:`Index.insert` raising when inserting ``None`` into :class:`Index` with ``dtype="string[pyarrow_numpy]"`` (:issue:`55365`)
 - Fixed bug in :meth:`Series.all`  and :meth:`Series.any` not treating missing values correctly for ``dtype="string[pyarrow_numpy]"`` (:issue:`55367`)
 - Fixed bug in :meth:`Series.rank` for ``string[pyarrow_numpy]`` dtype (:issue:`55362`)
-- Fixed bug in :meth:`Series.str.extractall` for ``string[pyarrow]`` dtype being converted to object (:issue:`53846`)
+- Fixed bug in :meth:`Series.str.extractall` for :class:`ArrowDtype` dtype being converted to object (:issue:`53846`)
 - Silence ``Period[B]`` warnings introduced by :issue:`53446` during normal plotting activity (:issue:`55138`)
 -
 

pandas/tests/strings/test_extract.py

@@ -2,6 +2,7 @@
 import re
 
 import numpy as np
+import pyarrow as pa
 import pytest
 
 from pandas import (
@@ -11,6 +12,7 @@
     Series,
     _testing as tm,
 )
+from pandas.core.dtypes.dtypes import ArrowDtype
 
 
 def test_extract_expand_kwarg_wrong_type_raises(any_string_dtype):
@@ -706,3 +708,18 @@ def test_extractall_same_as_extract_subject_index(any_string_dtype):
     has_match_index = s.str.extractall(pattern_one_noname)
     no_match_index = has_match_index.xs(0, level="match")
     tm.assert_frame_equal(extract_one_noname, no_match_index)
+
+
+@pytest.mark.parametrize(
+    "data, expected_dtype",
+    [
+        (Series(["abc", "ab"], dtype=ArrowDtype(pa.string())), "string[pyarrow]"),
+        (Series(["abc", "ab"], dtype="string"), "string[python]"),
+        (Series(["abc", "ab"]), "object"),
+    ]
+)
+def test_extractall_preserves_dtype(data, expected_dtype):
+    # Ensure that when extractall is called on a series with specific dtypes set, that
+    # the dtype is preserved in the resulting DataFrame's column.
+    result = data.str.extractall("(ab)")
+    assert result.dtypes[0] == expected_dtype