The word "testing" is a bit misleading. It's not about test coverage, it's about experimenting to find architecture decisions that are suitable for further development. So, not generating automated tests, but instead building throw-away features on top of the new thing and seeing if they turn out okay. (Though the post remains a bit vague on how to judge "okay".) Maybe it should be called something like "ephemeral build-out" or "future usage trial" or so.