TST: Added the new supported sorting algorithm stable to test

Addition to doc Fix PR: #38503

Implemented changes:
Parameterized tests with addition of the newly supported sorting method stable from numpy 1.15.0

Author: Damodara Puddu

pandas/tests/series/methods/test_sort_index.py

@@ -104,18 +104,13 @@ def test_sort_index_multiindex(self, level):
         res = s.sort_index(level=level, sort_remaining=False)
         tm.assert_series_equal(s, res)
 
-    def test_sort_index_kind(self):
+    @pytest.mark.parametrize("kind", ["quicksort", "mergesort", "heapsort", "stable"])
+    def test_sort_index_kind(self, kind):
         # GH#14444 & GH#13589:  Add support for sort algo choosing
         series = Series(index=[3, 2, 1, 4, 3], dtype=object)
         expected_series = Series(index=[1, 2, 3, 3, 4], dtype=object)
 
-        index_sorted_series = series.sort_index(kind="mergesort")
-        tm.assert_series_equal(expected_series, index_sorted_series)
-
-        index_sorted_series = series.sort_index(kind="quicksort")
-        tm.assert_series_equal(expected_series, index_sorted_series)
-
-        index_sorted_series = series.sort_index(kind="heapsort")
+        index_sorted_series = series.sort_index(kind=kind)
         tm.assert_series_equal(expected_series, index_sorted_series)
 
     def test_sort_index_na_position(self):
@@ -251,32 +246,22 @@ def test_sort_index_key_int(self):
         result = series.sort_index(key=lambda x: 2 * x)
         tm.assert_series_equal(result, series)
 
-    def test_sort_index_kind_key(self, sort_by_key):
+    @pytest.mark.parametrize("kind", ["quicksort", "mergesort", "heapsort", "stable"])
+    def test_sort_index_kind_key(self, kind, sort_by_key):
         # GH #14444 & #13589:  Add support for sort algo choosing
         series = Series(index=[3, 2, 1, 4, 3], dtype=object)
         expected_series = Series(index=[1, 2, 3, 3, 4], dtype=object)
 
-        index_sorted_series = series.sort_index(kind="mergesort", key=sort_by_key)
-        tm.assert_series_equal(expected_series, index_sorted_series)
-
-        index_sorted_series = series.sort_index(kind="quicksort", key=sort_by_key)
+        index_sorted_series = series.sort_index(kind=kind, key=sort_by_key)
         tm.assert_series_equal(expected_series, index_sorted_series)
 
-        index_sorted_series = series.sort_index(kind="heapsort", key=sort_by_key)
-        tm.assert_series_equal(expected_series, index_sorted_series)
-
-    def test_sort_index_kind_neg_key(self):
+    @pytest.mark.parametrize("kind", ["quicksort", "mergesort", "heapsort", "stable"])
+    def test_sort_index_kind_neg_key(self, kind):
         # GH #14444 & #13589:  Add support for sort algo choosing
         series = Series(index=[3, 2, 1, 4, 3], dtype=object)
         expected_series = Series(index=[4, 3, 3, 2, 1], dtype=object)
 
-        index_sorted_series = series.sort_index(kind="mergesort", key=lambda x: -x)
-        tm.assert_series_equal(expected_series, index_sorted_series)
-
-        index_sorted_series = series.sort_index(kind="quicksort", key=lambda x: -x)
-        tm.assert_series_equal(expected_series, index_sorted_series)
-
-        index_sorted_series = series.sort_index(kind="heapsort", key=lambda x: -x)
+        index_sorted_series = series.sort_index(kind=kind, key=lambda x: -x)
         tm.assert_series_equal(expected_series, index_sorted_series)
 
     def test_sort_index_na_position_key(self, sort_by_key):