change backward test function
change backward test function

nudles/incubator-singa,nudles/incubator-singa,nudles/incubator-singa,apache/incubator-singa,nudles/incubator-singa,apache/incubator-singa,apache/incubator-singa,apache/incubator-singa,apache/incubator-singa,nudles/incubator-singa