add comments in test_Expand.cpp
add comments in test_Expand.cpp

baidu/Paddle,Canpio/Paddle,lcy-seso/Paddle,chengduoZH/Paddle,lcy-seso/Paddle,PaddlePaddle/Paddle,lcy-seso/Paddle,tensor-tang/Paddle,luotao1/Paddle,luotao1/Paddle,Canpio/Paddle,QiJune/Paddle,jacquesqiao/Paddle,tensor-tang/Paddle,reyoung/Paddle,PaddlePaddle/Paddle,jacquesqiao/Paddle,putcn/Paddle,Canpio/Paddle,pkuyym/Paddle,Canpio/Paddle,baidu/Paddle,QiJune/Paddle,reyoung/Paddle,reyoung/Paddle,PaddlePaddle/Paddle,Canpio/Paddle,reyoung/Paddle,reyoung/Paddle,baidu/Paddle,putcn/Paddle,luotao1/Paddle,jacquesqiao/Paddle,jacquesqiao/Paddle,QiJune/Paddle,PaddlePaddle/Paddle,QiJune/Paddle,pkuyym/Paddle,lcy-seso/Paddle,luotao1/Paddle,baidu/Paddle,lcy-seso/Paddle,chengduoZH/Paddle,Canpio/Paddle,PaddlePaddle/Paddle,luotao1/Paddle,tensor-tang/Paddle,putcn/Paddle,QiJune/Paddle,luotao1/Paddle,pkuyym/Paddle,pkuyym/Paddle,chengduoZH/Paddle,jacquesqiao/Paddle,putcn/Paddle,lcy-seso/Paddle,Canpio/Paddle,putcn/Paddle,jacquesqiao/Paddle,chengduoZH/Paddle,reyoung/Paddle,tensor-tang/Paddle,QiJune/Paddle,putcn/Paddle,Canpio/Paddle,PaddlePaddle/Paddle,luotao1/Paddle,chengduoZH/Paddle,baidu/Paddle,pkuyym/Paddle,pkuyym/Paddle,tensor-tang/Paddle,PaddlePaddle/Paddle