test for issue #305, marked with xfail (#306)

tests/inputs/oneof/test_oneof.py

@@ -1,5 +1,10 @@
+import pytest
+
 import betterproto
-from tests.output_betterproto.oneof import Test
+from tests.output_betterproto.oneof import (
+    MixedDrink,
+    Test,
+)
 from tests.output_betterproto_pydantic.oneof import Test as TestPyd
 from tests.util import get_test_case_json_data
 
@@ -19,3 +24,20 @@ def test_which_name():
 def test_which_count_pyd():
     message = TestPyd(pitier="Mr. T", just_a_regular_field=2, bar_name="a_bar")
     assert betterproto.which_one_of(message, "foo") == ("pitier", "Mr. T")
+
+
+def test_oneof_constructor_assign():
+    message = Test(mixed_drink=MixedDrink(shots=42))
+    field, value = betterproto.which_one_of(message, "bar")
+    assert field == "mixed_drink"
+    assert value.shots == 42
+
+
+# Issue #305:
+@pytest.mark.xfail
+def test_oneof_nested_assign():
+    message = Test()
+    message.mixed_drink.shots = 42
+    field, value = betterproto.which_one_of(message, "bar")
+    assert field == "mixed_drink"
+    assert value.shots == 42