change data type of graph_test on test script to string.
change data type of graph_test on test script to string.

jongwook/incubator-s2graph,SteamShon/incubator-s2graph,SteamShon/incubator-s2graph,SteamShon/incubator-s2graph,jongwook/incubator-s2graph,daewon/incubator-s2graph,daewon/incubator-s2graph