Added test for github issue pandas-dev#33830 to test that categorical was preserving DateTimeIndex freq attribute

Author: andjhall

pandas/tests/indexes/datetimes/test_constructors.py

@@ -8,6 +8,7 @@
 
 import dateutil
 import numpy as np
+from pandas._testing.asserters import assert_equal
 import pytest
 import pytz
 
@@ -84,6 +85,16 @@ def test_categorical_preserves_tz(self):
                 result = DatetimeIndex(obj)
                 tm.assert_index_equal(result, dti)
 
+    def test_categorical_preserves_freq(self):
+        # GH33830 freq retention in categorical
+        dti = pd.date_range('2016-01-01', periods=5)
+        expected = dti.freq
+
+        cat = pd.Categorical(dti)
+        result = cat.categories.freq
+
+        assert expected == result
+
     def test_dti_with_period_data_raises(self):
         # GH#23675
         data = pd.PeriodIndex(["2016Q1", "2016Q2"], freq="Q")