TST: Added test for non-nano DTI intersection and updated whatsnew (#59280)

* TST: add intersection test non-nano

* modify whatsnew

Author: asishm

doc/source/whatsnew/v3.0.0.rst

@@ -507,7 +507,7 @@ Datetimelike
 - Bug in :meth:`Dataframe.agg` with df with missing values resulting in IndexError (:issue:`58810`)
 - Bug in :meth:`DatetimeIndex.is_year_start` and :meth:`DatetimeIndex.is_quarter_start` does not raise on Custom business days frequencies bigger then "1C" (:issue:`58664`)
 - Bug in :meth:`DatetimeIndex.is_year_start` and :meth:`DatetimeIndex.is_quarter_start` returning ``False`` on double-digit frequencies (:issue:`58523`)
-- Bug in :meth:`DatetimeIndex.union` when ``unit`` was non-nanosecond (:issue:`59036`)
+- Bug in :meth:`DatetimeIndex.union` and :meth:`DatetimeIndex.intersection` when ``unit`` was non-nanosecond (:issue:`59036`)
 - Bug in :meth:`Series.dt.microsecond` producing incorrect results for pyarrow backed :class:`Series`. (:issue:`59154`)
 - Bug in :meth:`to_datetime` not respecting dayfirst if an uncommon date string was passed. (:issue:`58859`)
 - Bug in setting scalar values with mismatched resolution into arrays with non-nanosecond ``datetime64``, ``timedelta64`` or :class:`DatetimeTZDtype` incorrectly truncating those scalars (:issue:`56410`)

pandas/tests/indexes/datetimes/test_setops.py

@@ -681,3 +681,16 @@ def test_union_non_nano_rangelike():
         freq="D",
     )
     tm.assert_index_equal(result, expected)
+
+
+def test_intersection_non_nano_rangelike():
+    # GH 59271
+    l1 = date_range("2024-01-01", "2024-01-03", unit="s")
+    l2 = date_range("2024-01-02", "2024-01-04", unit="s")
+    result = l1.intersection(l2)
+    expected = DatetimeIndex(
+        ["2024-01-02", "2024-01-03"],
+        dtype="datetime64[s]",
+        freq="D",
+    )
+    tm.assert_index_equal(result, expected)