Add parametrization of name, simplify expected construction

Author: Mateusz Górski

pandas/tests/indexes/datetimes/test_datetime.py

@@ -458,15 +458,18 @@ def test_to_frame_datetime_tz(self):
         expected = DataFrame(idx, index=idx)
         tm.assert_frame_equal(result, expected)
 
-    def test_index_map(self):
+    @pytest.mark.parametrize("name", [None, "name"])
+    def test_index_map(self, name):
         # see GH20990
         count = 6
-        index = pd.date_range("2018-01-01", periods=count, freq="M", name="name")
+        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))
 
-        df = pd.DataFrame([[2018, i + 1] for i in range(6)], columns=["name", "name"])
-        exp_index = pd.MultiIndex.from_frame(df)
+        exp_index = pd.MultiIndex.from_arrays(
+            [[2018 for i in range(count)], [i for i in range(1, count + 1)]],
+            names=[name, name],
+        )
         expected = pd.Series(np.arange(count), index=exp_index)
 
         tm.assert_series_equal(a, expected)