TST: Add tests for Categorical.is_dtype_equal against Series (#19045)

Author: jschendel

pandas/tests/categorical/test_dtypes.py

@@ -6,7 +6,7 @@
 
 import pandas.util.testing as tm
 from pandas.core.dtypes.dtypes import CategoricalDtype
-from pandas import Categorical, Index, CategoricalIndex
+from pandas import Categorical, Index, CategoricalIndex, Series
 
 
 class TestCategoricalDtypes(object):
@@ -30,6 +30,17 @@ def test_is_equal_dtype(self):
             CategoricalIndex(c1, categories=list('cab'))))
         assert not c1.is_dtype_equal(CategoricalIndex(c1, ordered=True))
 
+        # GH 16659
+        s1 = Series(c1)
+        s2 = Series(c2)
+        s3 = Series(c3)
+        assert c1.is_dtype_equal(s1)
+        assert c2.is_dtype_equal(s2)
+        assert c3.is_dtype_equal(s3)
+        assert c1.is_dtype_equal(s2)
+        assert not c1.is_dtype_equal(s3)
+        assert not c1.is_dtype_equal(s1.astype(object))
+
     def test_set_dtype_same(self):
         c = Categorical(['a', 'b', 'c'])
         result = c._set_dtype(CategoricalDtype(['a', 'b', 'c']))