Update tests in test_custom_type_setup.cpp

Author: XuehaiPan

tests/test_custom_type_setup.cpp

@@ -26,13 +26,21 @@ TEST_SUBMODULE(custom_type_setup, m) {
             auto *type = &heap_type->ht_type;
             type->tp_flags |= Py_TPFLAGS_HAVE_GC;
             type->tp_traverse = [](PyObject *self_base, visitproc visit, void *arg) {
-                auto &self = py::cast<OwnsPythonObjects &>(py::handle(self_base));
-                Py_VISIT(self.value.ptr());
+        // https://docs.python.org/3/c-api/typeobj.html#c.PyTypeObject.tp_traverse
+#if PY_VERSION_HEX >= 0x03090000 // Python 3.9
+                Py_VISIT(Py_TYPE(self_base));
+#endif
+                if (py::detail::is_holder_constructed(self_base)) {
+                    auto &self = py::cast<OwnsPythonObjects &>(py::handle(self_base));
+                    Py_VISIT(self.value.ptr());
+                }
                 return 0;
             };
             type->tp_clear = [](PyObject *self_base) {
-                auto &self = py::cast<OwnsPythonObjects &>(py::handle(self_base));
-                self.value = py::none();
+                if (py::detail::is_holder_constructed(self_base)) {
+                    auto &self = py::cast<OwnsPythonObjects &>(py::handle(self_base));
+                    self.value = py::none();
+                }
                 return 0;
             };
         }));