TST: Added test for frequency retention in categorical constructor (#46779)

* Added test for github issue #33830 to test that categorical was preserving DateTimeIndex freq attribute

* Added an additional test for value_counts preserving frequency

* Modified tests in test_constructors.py to pass the pre-commit check

* Removed tests from test_constructors that were not needed

* Moved categorical freq retention test to pandas/tests/arrays/categorical/

Co-authored-by: Brian Gollop <[email protected]>

Author: andjhall

pandas/tests/arrays/categorical/test_constructors.py

@@ -759,3 +759,14 @@ def test_constructor_datetime64_non_nano(self):
 
         cat = Categorical(values, categories=categories)
         assert (cat == values).all()
+
+    def test_constructor_preserves_freq(self):
+        # GH33830 freq retention in categorical
+        dti = date_range("2016-01-01", periods=5)
+
+        expected = dti.freq
+
+        cat = Categorical(dti)
+        result = cat.categories.freq
+
+        assert expected == result