add tests for PyInstanceMethod_Type
diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index 940605e..b1cb6fe 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -1231,6 +1231,8 @@
 	PyModule_AddObject(m, "PY_SSIZE_T_MAX", PyLong_FromSsize_t(PY_SSIZE_T_MAX));
 	PyModule_AddObject(m, "PY_SSIZE_T_MIN", PyLong_FromSsize_t(PY_SSIZE_T_MIN));
 	PyModule_AddObject(m, "SIZEOF_PYGC_HEAD", PyLong_FromSsize_t(sizeof(PyGC_Head)));
+	Py_INCREF(&PyInstanceMethod_Type);
+	PyModule_AddObject(m, "instancemethod", (PyObject *)&PyInstanceMethod_Type);
 
 	TestError = PyErr_NewException("_testcapi.error", NULL, NULL);
 	Py_INCREF(TestError);