Add test for pandas-devGH-43321

Author: johannes-mueller

pandas/tests/frame/test_arithmetic.py

@@ -1061,6 +1061,30 @@ def test_frame_single_columns_object_sum_axis_1():
     tm.assert_series_equal(result, expected)
 
 
+def test_frame_multi_index_operations():
+    # GH 43321
+    df = DataFrame(
+        {2010: [1, 2, 3], 2020: [3, 4, 5]},
+        index=MultiIndex.from_product(
+            [["a"], ["b"], [0, 1, 2]], names=["scen", "mod", "id"]
+        ),
+    )
+
+    s = Series(
+        [0.4],
+        index=MultiIndex.from_product([["b"], ["a"]], names=["mod", "scen"]),
+    )
+
+    expected = DataFrame(
+        {2010: [1.4, 2.4, 3.4], 2020: [3.4, 4.4, 5.4]},
+        index=MultiIndex.from_product(
+            [["a"], ["b"], [0, 1, 2]], names=["scen", "mod", "id"]
+        ),
+    )
+
+    tm.assert_frame_equal(df.add(s, axis=0), expected)
+
+
 # -------------------------------------------------------------------
 # Unsorted
 #  These arithmetic tests were previously in other files, eventually