TST: add test to verify column does not lose categorical type when using loc (pandas-dev#37988)

Author: fgebhart

pandas/tests/indexing/test_loc.py

@@ -12,6 +12,7 @@
 
 import pandas as pd
 from pandas import (
+    Categorical,
     CategoricalIndex,
     DataFrame,
     Index,
@@ -1319,6 +1320,13 @@ def test_loc_setitem_datetime_keys_cast(self):
             expected = DataFrame({"one": [100.0, 200.0]}, index=[dt1, dt2])
             tm.assert_frame_equal(df, expected)
 
+    def test_loc_setitem_categorical_column_retains_dtype(self, ordered):
+        # GH16360
+        result = DataFrame({"A": [1]})
+        result.loc[:, "B"] = Categorical(["b"], ordered=ordered)
+        expected = DataFrame({"A": [1], "B": Categorical(["b"], ordered=ordered)})
+        tm.assert_frame_equal(result, expected)
+
 
 class TestLocCallable:
     def test_frame_loc_getitem_callable(self):