BUG: Fix assert_series_equal with check_category_order=False for categoricals with nulls

- Use allow_fill=True and fill_value=np.nan in take() to handle null codes properly
- Add regression testcase test_assert_series_equal_categorical_nulls_different_order
- Closes #62008

Author: anishkarki

pandas/_testing/asserters.py

@@ -495,8 +495,8 @@ 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),
+            left.categories.take(left.codes, allow_fill=True, fill_value=np.nan),
+            right.categories.take(right.codes, allow_fill=True, fill_value=np.nan),
             obj=f"{obj}.values",
             exact=exact,
         )

pandas/tests/util/test_assert_series_equal.py

@@ -507,3 +507,19 @@ def test_assert_series_equal_check_exact_index_default(left_idx, right_idx):
     ser2 = Series(np.zeros(6, dtype=int), right_idx)
     tm.assert_series_equal(ser1, ser2)
     tm.assert_frame_equal(ser1.to_frame(), ser2.to_frame())
+
+
+def test_assert_series_equal_categorical_nulls_different_order():
+    # https://github.com/pandas-dev/pandas/issues/62008
+    values = ["B", np.nan, "D"]
+    categorical_left = ["B", "D"]
+    categorical_right = categorical_left[::-1]  # Different Order
+
+    left = Series(Categorical(values, categories=categorical_left))
+    right = Series(Categorical(values, categories=categorical_right))
+
+    tm.assert_series_equal(left, right, check_category_order=False)
+
+    msg = "Categorical.categories are different"
+    with pytest.raises(AssertionError, match=msg):
+        tm.assert_series_equal(left, right, check_category_order=True)