BUG: assert_index_equal CategoricalIndex incomparable categories gives AssertionError

Author: Aniketsy

doc/source/whatsnew/v3.0.0.rst

@@ -936,7 +936,8 @@ Categorical
 - Bug in :meth:`Categorical.astype` where ``copy=False`` would still trigger a copy of the codes (:issue:`62000`)
 - Bug in :meth:`DataFrame.pivot` and :meth:`DataFrame.set_index` raising an ``ArrowNotImplementedError`` for columns with pyarrow dictionary dtype (:issue:`53051`)
 - Bug in :meth:`Series.convert_dtypes` with ``dtype_backend="pyarrow"`` where empty :class:`CategoricalDtype` :class:`Series` raised an error or got converted to ``null[pyarrow]`` (:issue:`59934`)
--
+- Bug in :func:`testing.assert_index_equal` raising ``TypeError`` instead of ``AssertionError`` for incomparable ``CategoricalIndex`` when ``check_categorical=True`` and ``exact=False`` (:issue:`61935`)
+- 
 
 Datetimelike
 ^^^^^^^^^^^^

pandas/_testing/asserters.py

@@ -38,7 +38,6 @@
 import pandas as pd
 from pandas import (
     Categorical,
-    CategoricalIndex,
     DataFrame,
     DatetimeIndex,
     Index,
@@ -326,15 +325,16 @@ def _check_types(left, right, obj: str = "Index") -> None:
     # skip exact index checking when `check_categorical` is False
     elif check_exact and check_categorical:
         if not left.equals(right):
+            # _values compare can raise TypeError for non-comparable categoricals (GH#61935)
             try:
                 mismatch = left._values != right._values
             except TypeError:
-                if isinstance(left, CategoricalIndex) and isinstance(
-                    right, CategoricalIndex
-                ):
-                    mismatch = left.codes != right.codes
-                else:
-                    mismatch = left.values != right.values
+                raise_assert_detail(
+                    obj,
+                    "types are not comparable (non-matching categorical categories)",
+                    left,
+                    right,
+                )
 
             if not isinstance(mismatch, np.ndarray):
                 mismatch = cast("ExtensionArray", mismatch).fillna(True)

pandas/tests/util/test_assert_index_equal.py

@@ -319,25 +319,9 @@ def test_assert_multi_index_dtype_check_categorical(check_categorical):
         tm.assert_index_equal(idx1, idx2, check_categorical=check_categorical)
 
 
-def test_assert_index_equal_categorical_mismatch_categories():
-    # GH#61941 - CategoricalIndex vs Index
-    ci = CategoricalIndex(["a", "b", "c"], categories=["a", "b", "c"], ordered=False)
-    idx = Index(["a", "b", "c"])
-
-    with pytest.raises(AssertionError, match="Index are different"):
-        tm.assert_index_equal(
-            ci,
-            idx,
-        )
-
-
-def test_assert_categorical_index_equal_mismatch_categories():
-    # GH#61941 - both left and right are CategoricalIndex
-    ci1 = CategoricalIndex(["a", "b", "c"], categories=["a", "b", "c"], ordered=False)
-    ci2 = CategoricalIndex(["a", "b", "c"], categories=["a", "b", "d"], ordered=False)
-
-    with pytest.raises(AssertionError, match="Index are different"):
-        tm.assert_index_equal(
-            ci1,
-            ci2,
-        )
+def test_assert_index_equal_categorical_incomparable_categories():
+    # GH#61935
+    left = Index([1, 2, 3], name="a", dtype="category")
+    right = Index([1, 2, 6], name="a", dtype="category")
+    with pytest.raises(AssertionError, match="types are not comparable"):
+        tm.assert_index_equal(left, right, check_categorical=True, exact=False)