Add PY_SSIZE_T_MIN/MAX to _testcapi.

Modules/_testcapimodule.c

@@ -704,8 +704,10 @@ init_testcapi(void)
 	PyModule_AddObject(m, "ULONG_MAX", PyLong_FromUnsignedLong(ULONG_MAX));
 	PyModule_AddObject(m, "INT_MIN", PyInt_FromLong(INT_MIN));
 	PyModule_AddObject(m, "LONG_MIN", PyInt_FromLong(LONG_MIN));
+	PyModule_AddObject(m, "PY_SSIZE_T_MIN", PyInt_FromSsize_t(PY_SSIZE_T_MIN));
 	PyModule_AddObject(m, "INT_MAX", PyInt_FromLong(INT_MAX));
 	PyModule_AddObject(m, "LONG_MAX", PyInt_FromLong(LONG_MAX));
+	PyModule_AddObject(m, "PY_SSIZE_T_MAX", PyInt_FromSsize_t(PY_SSIZE_T_MAX));
 
 	TestError = PyErr_NewException("_testcapi.error", NULL, NULL);
 	Py_INCREF(TestError);