SDL Web8 support selenium testing tool for automation testing? any one have idea...
Have you seen the post below, although written for 2013, the principles should still apply for Web 8, see Andrey Marchuk's answer:
Also Dominic Cronin provides a brief and concise direction in his blog post: http://www.dominic.cronin.nl/weblog/on-line-resources-for-the-agile-tridion-development-talk
The article even includes the (coded) demo given during the 2014 Tridion Developer Summit along with the slides discussing various approaches for automated testing.