fixup! Add (failing) roundtrip test for const unique_ptr reference

Author: rhaschke

tests/test_class_sh_basic.py

@@ -158,7 +158,18 @@ def test_unique_ptr_consumer_roundtrip(pass_f, rtrn_f, moved_out, moved_in):
 )
 @pytest.mark.parametrize(
     "pass_f",
-    [m.consumer.pass_uq_cref, m.consumer.pass_cptr, m.consumer.pass_cref],
+    [
+        # This fails with: ValueError: Cannot disown non-owning holder (loaded_as_unique_ptr).
+        #
+        # smart_holder_type_caster_load<T>::loaded_as_unique_ptr() attempts to pass
+        # the not-owned cref as a new unique_ptr, which would eventually destroy the object,
+        # and is thus (correctly) suppressed.
+        # To fix this, smart_holder would need to store the (original) unique_ptr reference,
+        # e.g. using a union of unique_ptr + shared_ptr.
+        pytest.param(m.consumer.pass_uq_cref, marks=pytest.mark.xfail),
+        m.consumer.pass_cptr,
+        m.consumer.pass_cref,
+    ],
 )
 def test_unique_ptr_cref_consumer_roundtrip(rtrn_f, pass_f):
     c = m.consumer()
@@ -168,16 +179,6 @@ def test_unique_ptr_cref_consumer_roundtrip(rtrn_f, pass_f):
 
     c.pass_uq_valu(passenger)  # moves passenger to C++  (checked above)
 
-    if pass_f == m.consumer.pass_uq_cref:
-        # This fails with: ValueError: Cannot disown non-owning holder (loaded_as_unique_ptr).
-        #
-        # smart_holder_type_caster_load<T>::loaded_as_unique_ptr() attempts to pass
-        # the not-owned cref as a new unique_ptr, which would eventually destroy the object,
-        # and is thus (correctly) suppressed.
-        # To fix this, smart_holder would need to store the (original) unique_ptr reference,
-        # e.g. using a union of unique_ptr + shared_ptr.
-        pytest.xfail()
-
     for _ in range(10):
         cref = rtrn_f(c)  # fetches const reference, should keep-alive parent c
         assert pass_f(c, cref) == mtxt_orig