fixup test_scalar

Author: MarcoGorelli

pandas/tests/indexing/test_scalar.py

@@ -205,7 +205,10 @@ def test_mixed_index_at_iat_loc_iloc_dataframe(self):
     def test_iat_setter_incompatible_assignment(self):
         # GH 23236
         result = DataFrame({"a": [0, 1], "b": [4, 5]})
-        result.iat[0, 0] = None
+        with tm.assert_produces_warning(
+            FutureWarning, match="item of incompatible dtype"
+        ):
+            result.iat[0, 0] = None
         expected = DataFrame({"a": [None, 1], "b": [4, 5]})
         tm.assert_frame_equal(result, expected)