Add a test to avoid more regressions.

Lib/test/test_capi/test_misc.py

@@ -1593,6 +1593,39 @@ def test_module_state_shared_in_global(self):
         self.assertEqual(main_attr_id, subinterp_attr_id)
 
 
+class BuiltinStaticTypesTests(unittest.TestCase):
+
+    TYPES = [
+        object,
+        type,
+        int,
+        str,
+        dict,
+        type(None),
+        bool,
+        BaseException,
+        Exception,
+        Warning,
+        DeprecationWarning,  # Warning subclass
+    ]
+
+    def test_tp_bases_is_set(self):
+        # PyTypeObject.tp_bases is documented as public API.
+        # See https://github.com/python/cpython/issues/105020.
+        for typeobj in self.TYPES:
+            with self.subTest(typeobj):
+                bases = _testcapi.type_get_tp_bases(typeobj)
+                self.assertIsNot(bases, None)
+
+    def test_tp_mro_is_set(self):
+        # PyTypeObject.tp_bases is documented as public API.
+        # See https://github.com/python/cpython/issues/105020.
+        for typeobj in self.TYPES:
+            with self.subTest(typeobj):
+                mro = _testcapi.type_get_tp_mro(typeobj)
+                self.assertIsNot(mro, None)
+
+
 class TestThreadState(unittest.TestCase):
 
     @threading_helper.reap_threads

Modules/_testcapimodule.c

@@ -2606,6 +2606,27 @@ type_assign_version(PyObject *self, PyObject *type)
 }
 
 
+static PyObject *
+type_get_tp_bases(PyObject *self, PyObject *type)
+{
+    PyObject *bases = ((PyTypeObject *)type)->tp_bases;
+    if (bases == NULL) {
+        Py_RETURN_NONE;
+    }
+    return Py_NewRef(bases);
+}
+
+static PyObject *
+type_get_tp_mro(PyObject *self, PyObject *type)
+{
+    PyObject *mro = ((PyTypeObject *)type)->tp_mro;
+    if (mro == NULL) {
+        Py_RETURN_NONE;
+    }
+    return Py_NewRef(mro);
+}
+
+
 // Test PyThreadState C API
 static PyObject *
 test_tstate_capi(PyObject *self, PyObject *Py_UNUSED(args))
@@ -3361,6 +3382,8 @@ static PyMethodDef TestMethods[] = {
     {"test_py_is_funcs", test_py_is_funcs, METH_NOARGS},
     {"type_get_version", type_get_version, METH_O, PyDoc_STR("type->tp_version_tag")},
     {"type_assign_version", type_assign_version, METH_O, PyDoc_STR("PyUnstable_Type_AssignVersionTag")},
+    {"type_get_tp_bases", type_get_tp_bases, METH_O},
+    {"type_get_tp_mro", type_get_tp_mro, METH_O},
     {"test_tstate_capi", test_tstate_capi, METH_NOARGS, NULL},
     {"frame_getlocals", frame_getlocals, METH_O, NULL},
     {"frame_getglobals", frame_getglobals, METH_O, NULL},