Add test that fails only when to_datetime gets cache=True

Author: vnlitvinov

pandas/tests/indexes/datetimes/test_tools.py

@@ -469,6 +469,19 @@ def test_to_datetime_tz(self, cache):
         with pytest.raises(ValueError, match=msg):
             pd.to_datetime(arr, cache=cache)
 
+
+    @pytest.mark.parametrize('cache', [True, False])
+    def test_to_datetime_offset(self, cache):
+        # inspired by asv timeseries.ToDatetimeNONISO8601 benchmark
+        # see GH-26097 for more
+        ts_string_1 = 'March 1, 2018 12:00:00+0400'
+        ts_string_2 = 'March 1, 2018 12:00:00+0500'
+        arr = [ts_string_1] * 5 + [ts_string_2] * 5
+        expected = pd.Index([parse(x) for x in arr])
+        result = pd.to_datetime(arr, cache=cache)
+        tm.assert_index_equal(result, expected)
+
+
     @pytest.mark.parametrize('cache', [True, False])
     def test_to_datetime_tz_pytz(self, cache):
         # see gh-8260