Adding unit tests for checking that closing unbuffered channel closes all blocked senders and receivers (#8067)
Adding unit tests for checking that closing unbuffered channel closes all blocked senders and receivers (#8067)

* Adding unit tests for checking that closing unbuffered channel closes all blocked senders and receivers

* Fixing sleep time

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