For the ones interested in testing, you can wait for he actual launch which includes the free version and you don't have to pay anything. Stadia will be implemented in a way that when you are watching a video of a game on youtube, there will be a stadia button that will allow you to buy a game or test the demo. So testing the demo will cost nothing, a click from YT and imediately stream the game demo.
remember, Amazon is also planning to build a streaming platform, and they can make use of twitch to do such features stadia will do on top of youtube.
Last edited by CuCabeludo - on 24 October 2019