常用测试文件
https://tse1-mm.cn.bing.net/th/id/OIP-C.Russj_ScHRzeGEodKscxEgHaEo?pid=ImgDet&rs=1
https://unsplash.com/photos/qhixfmpqN8s/download?force=true&w=1920
https://unsplash.com/photos/lL5qdPjHbeE/download?force=true&w=2400
https://unsplash.com/photos/2_l0WMA9Ha0/download?force=true&w=6024
http://cachefly.cachefly.net/10mb.test
http://cachefly.cachefly.net/50mb.test
http://cachefly.cachefly.net/100mb.test