ENH: gb.is_monotonic_increasing pandas-dev#17015 fix test format, whatsnew format

Author: No-Stream

doc/source/whatsnew/v0.21.1.txt

@@ -22,7 +22,7 @@ Other Enhancements
 ^^^^^^^^^^^^^^^^^^
 
 - :meth:`Timestamp.timestamp` is now available in Python 2.7. (:issue:`17329`)
-- :func: groupby.is_monotonic_increasing and .is_monotonic_decreasing extend Series.is_monotonic_increasing to groups, returning whether each group is monotonically increasing or decreasing, respectively. (:issue:`17015`)
+- :meth:`groupby.is_monotonic_increasing()` and :meth:`.is_monotonic_decreasing()` extend :meth:`Series.is_monotonic_increasing()` to groups. (:issue:`17015`)
 -
 
 .. _whatsnew_0211.deprecations:

pandas/tests/groupby/test_groupby.py

@@ -2611,10 +2611,8 @@ def test_is_monotonic_increasing(self, in_vals, out_vals):
             'C': in_vals}
         df = pd.DataFrame(source_dict)
         result = df.groupby(['B']).C.is_monotonic_increasing()
-        expected = pd.Series(index=['a', 'b', 'c', 'd'],
-                             data=out_vals,
-                             name='C')
-        expected.index.name = 'B'
+        index = pd.Index(list('abcd'), name='B')
+        expected = pd.Series(index=index, data=out_vals, name='C')
         tm.assert_series_equal(result, expected)
 
         # Also check result equal to manually taking x.is_monotonic_increasing.
@@ -2642,11 +2640,9 @@ def test_is_monotonic_decreasing(self, in_vals, out_vals):
             'C': in_vals}
 
         df = pd.DataFrame(source_dict)
-        result = df.groupby('B').C.is_monotonic_decreasing()
-        expected = pd.Series(index=['a', 'b', 'c', 'd'],
-                             data=out_vals,
-                             name='C')
-        expected.index.name = 'B'
+        result = df.groupby(['B']).C.is_monotonic_decreasing()
+        index = pd.Index(list('abcd'), name='B')
+        expected = pd.Series(index=index, data=out_vals, name='C')
         tm.assert_series_equal(result, expected)
 
     def test_apply_numeric_coercion_when_datetime(self):