evaluator: change string test. (#2302)
evaluator: change string test. (#2302)


ueizhou/tidb,zs634134578/tidb,cosmtrek/tidb,tiancaiamao/tidb,coocood/tidb,andelf/tidb,kyle-wang/tidb,astaxie/tidb,mccxj/tidb,zs634134578/tidb,Cofyc/tidb,EvilMcJerkface/tidb,pingcap/tidb,c4pt0r/tidb,simon-xia/tidb,c4pt0r/tidb,XuHuaiyu/tidb,8cbx/tidb,gaocegege/tidb,qhsong/tidb,qiuyesuifeng/tidb,kyle-wang/tidb,ngaut/tidb,liyu4/tidb,yangwenmai/tidb,coocood/tidb,c4pt0r/tidb,EvilMcJerkface/tidb,yuanwhy/tidb,ueizhou/tidb,ming-relax/tidb,yuanwhy/tidb,JinheLin/tidb,wusphinx/tidb,louishust/tidb,pingcap/tidb,ming-relax/tidb,ngaut/tidb,gaocegege/tidb,spongedu/tidb,silenceper/tidb,c4pt0r/tidb,pingcap/tidb,ngaut/tidb,kyle-wang/tidb,CodeRushing/tidb,JinheLin/tidb,simon-xia/tidb,pingcap/tidb,8cbx/tidb,Cofyc/tidb,silenceper/tidb,zimulala/tidb,spongedu/tidb,wusphinx/tidb,andelf/tidb,CodeRushing/tidb,cosmtrek/tidb,ngaut/tidb,anywhy/tidb,myrice/tidb,louishust/tidb,zimulala/tidb,pingcap/tidb,c4pt0r/tidb,c4pt0r/tidb,tiancaiamao/tidb,kyle-wang/tidb,kyle-wang/tidb,myrice/tidb,ngaut/tidb,XuHuaiyu/tidb,qiuyesuifeng/tidb,liyu4/tidb,silentred/tidb,mccxj/tidb,silentred/tidb,pingcap/tidb,astaxie/tidb,Nify/tidb,ngaut/tidb,Nify/tidb,anywhy/tidb,qhsong/tidb,kyle-wang/tidb,yangwenmai/tidb