there’s also a talk from the same author (German Velasco) that’s already pointed to above, see here: https://www.youtube.com/watch?v=h8NURVLysrk
And he has another blog post https://www.germanvelasco.com/blog/using-has-element-for-better-liveviewtest-assertions
Another thing that could help you is this: https://github.com/dashbitco/bytepack_archive/tree/main/apps/bytepack_web/test/bytepack_web/live The source code behind bytepack from the ‘makers’ themselves AFAICS it’s not using any headless browsers so could help you to see how they are doing it.