done

lib/python3.11/site-packages/pandas/tests/indexes/datetimes/test_arithmetic.py

@@ -0,0 +1,56 @@
+# Arithmetic tests specific to DatetimeIndex are generally about `freq`
+#  rentention or inference.  Other arithmetic tests belong in
+#  tests/arithmetic/test_datetime64.py
+import pytest
+
+from pandas import (
+    Timedelta,
+    TimedeltaIndex,
+    Timestamp,
+    date_range,
+    timedelta_range,
+)
+import pandas._testing as tm
+
+
+class TestDatetimeIndexArithmetic:
+    def test_add_timedelta_preserves_freq(self):
+        # GH#37295 should hold for any DTI with freq=None or Tick freq
+        tz = "Canada/Eastern"
+        dti = date_range(
+            start=Timestamp("2019-03-26 00:00:00-0400", tz=tz),
+            end=Timestamp("2020-10-17 00:00:00-0400", tz=tz),
+            freq="D",
+        )
+        result = dti + Timedelta(days=1)
+        assert result.freq == dti.freq
+
+    def test_sub_datetime_preserves_freq(self, tz_naive_fixture):
+        # GH#48818
+        dti = date_range("2016-01-01", periods=12, tz=tz_naive_fixture)
+
+        res = dti - dti[0]
+        expected = timedelta_range("0 Days", "11 Days")
+        tm.assert_index_equal(res, expected)
+        assert res.freq == expected.freq
+
+    @pytest.mark.xfail(
+        reason="The inherited freq is incorrect bc dti.freq is incorrect "
+        "https://github.com/pandas-dev/pandas/pull/48818/files#r982793461"
+    )
+    def test_sub_datetime_preserves_freq_across_dst(self):
+        # GH#48818
+        ts = Timestamp("2016-03-11", tz="US/Pacific")
+        dti = date_range(ts, periods=4)
+
+        res = dti - dti[0]
+        expected = TimedeltaIndex(
+            [
+                Timedelta(days=0),
+                Timedelta(days=1),
+                Timedelta(days=2),
+                Timedelta(days=2, hours=23),
+            ]
+        )
+        tm.assert_index_equal(res, expected)
+        assert res.freq == expected.freq