Remove Series from test

Author: Mateusz Górski

pandas/tests/indexes/datetimes/test_datetime.py

@@ -462,13 +462,10 @@ def test_to_frame_datetime_tz(self):
     def test_index_map(self, name):
         # see GH20990
         count = 6
-        index = pd.date_range("2018-01-01", periods=count, freq="M", name=name)
-        a = pd.Series(np.arange(count), index=index)
-        a.index = a.index.map(lambda x: (x.year, x.month))
-
+        index = pd.date_range("2018-01-01", periods=count, freq="M", name=name).map(
+            lambda x: (x.year, x.month)
+        )
         exp_index = pd.MultiIndex.from_product(
             ((2018,), range(1, 7)), names=[name, name]
         )
-        expected = pd.Series(np.arange(count), index=exp_index)
-
-        tm.assert_series_equal(a, expected)
+        tm.assert_index_equal(index, exp_index)