BUG: Fix assert_series_equal for categoricals with nulls and check_category_order=False (#62008)

Author: Aniketsy

pandas/_testing/asserters.py

@@ -495,8 +495,15 @@ def assert_categorical_equal(
             lc, rc = left.categories, right.categories
         assert_index_equal(lc, rc, obj=f"{obj}.categories", exact=exact)
         assert_index_equal(
-            left.categories.take(left.codes),
-            right.categories.take(right.codes),
+            Index(
+                [left.categories[code] if code >= 0 else np.nan for code in left.codes]
+            ),
+            Index(
+                [
+                    right.categories[code] if code >= 0 else np.nan
+                    for code in right.codes
+                ]
+            ),
             obj=f"{obj}.values",
             exact=exact,
         )

pandas/tests/util/test_assert_categorical_equal.py

@@ -1,3 +1,4 @@
+import numpy as np
 import pytest
 
 from pandas import Categorical
@@ -86,3 +87,14 @@ def test_categorical_equal_object_override(obj):
 
     with pytest.raises(AssertionError, match=msg):
         tm.assert_categorical_equal(c1, c2, obj=obj)
+
+
+def test_categorical_equal_with_nans_and_different_order():
+    values = ["B", np.nan, "D"]
+    categories_left = ["B", "D"]
+    categories_right = categories_left[::-1]
+
+    left = Categorical(values, categories=categories_left)
+    right = Categorical(values, categories=categories_right)
+
+    tm.assert_categorical_equal(left, right, check_category_order=False)