update

Author: TomAugspurger

pandas/core/categorical.py

@@ -222,6 +222,7 @@ class Categorical(PandasObject):
     Categorical.order
     Categorical.min
     Categorical.max
+    pandas.api.types.CategoricalDtype
     """
 
     # For comparisons, so that numpy uses our implementation if the compare

pandas/tests/dtypes/test_dtypes.py

@@ -615,6 +615,9 @@ def test_invalid_raises(self):
         with tm.assert_raises_regex(TypeError, 'ordered'):
             CategoricalDtype(['a', 'b'], ordered='foo')
 
+        with tm.assert_raises_regex(TypeError, 'collection'):
+            CategoricalDtype('category')
+
     def test_mixed(self):
         a = CategoricalDtype(['a', 'b', 1, 2])
         b = CategoricalDtype(['a', 'b', '1', '2'])

pandas/util/testing.py

@@ -1244,9 +1244,11 @@ def assert_series_equal(left, right, check_dtype=True,
                        obj='{obj}.index'.format(obj=obj))
 
     if check_dtype:
+        # We want to skip exact dtype checking when `check_categorical`
+        # is False. We'll still raise if only one is a `Categorical`,
+        # regardless of `check_categorical`
         if (is_categorical_dtype(left) and is_categorical_dtype(right) and
                 not check_categorical):
-            # compat with pandas 0.21.0 CategoricalDtype
             pass
         else:
             assert_attr_equal('dtype', left, right)