move test and compare with expected df

Author: fgebhart

pandas/tests/dtypes/test_dtypes.py

@@ -998,10 +998,3 @@ def test_period_dtype_compare_to_string():
     dtype = PeriodDtype(freq="M")
     assert (dtype == "period[M]") is True
     assert (dtype != "period[M]") is False
-
-
-def test_column_not_loses_categorical_when_using_loc():
-    # GH16360
-    df = pd.DataFrame({"A": [1]})
-    df.loc[:, "B"] = Categorical(["a"])
-    assert is_categorical_dtype(df["B"])

pandas/tests/frame/indexing/test_categorical.py

@@ -386,3 +386,12 @@ def test_loc_indexing_preserves_index_category_dtype(self):
 
         result = df.loc[["a"]].index.levels[0]
         tm.assert_index_equal(result, expected)
+
+
+def test_column_not_loses_categorical_when_using_loc():
+    # GH16360
+    result = DataFrame({"A": [1]})
+    result.loc[:, "B"] = Categorical(["b"])
+    expected = DataFrame({"A": [1], "B": ["b"]})
+    expected["B"] = expected["B"].astype("category")
+    tm.assert_frame_equal(result, expected)