Fix setting of categories order when dtype is passed to a `Categori…

…calColumn` (#13955)

closes #13947 

This PR fixes the setting of categories in the appropriate order when a dtype with the same categories but of mismatching order is passed.

Authors:
  - GALI PREM SAGAR (https://github.com/galipremsagar)

Approvers:
  - Lawrence Mitchell (https://github.com/wence-)

URL: #13955

python/cudf/cudf/core/column/categorical.py

@@ -1483,7 +1483,7 @@ def set_categories(
                     ),
                 )
             elif (
-                not out_col._categories_equal(new_categories, ordered=ordered)
+                not out_col._categories_equal(new_categories, ordered=True)
                 or not self.ordered == ordered
             ):
                 out_col = out_col._set_categories(

python/cudf/cudf/tests/test_categorical.py

@@ -926,3 +926,13 @@ def test_categorical_string_index_contains(data, value):
     pidx = idx.to_pandas()
 
     assert_eq(value in idx, value in pidx)
+
+
+def test_categorical_index_with_dtype():
+    dtype = cudf.CategoricalDtype(categories=["a", "z", "c"])
+    gi = cudf.Index(["z", "c", "a"], dtype=dtype)
+    pi = pd.Index(["z", "c", "a"], dtype=dtype.to_pandas())
+
+    assert_eq(gi, pi)
+    assert_eq(gi.dtype, pi.dtype)
+    assert_eq(gi.dtype.categories, pi.dtype.categories)