The real question is even higher. Why should we measure knowledge?

If it's learning for the joy of learning you don't need a test. If it's to get a piece of paper you need for a job, then schools are just shitty interviews mostly uncorrelated to real world tasks.

I think we should move to learning for the sake of learning (free, open door lessons or pick your own on the internet at your own time - no frontal lessons but still provide a space for students to socialise) and give the chance to students to work on projects that can prove they know something. Workplaces can look at these projects and find someone who fit with them.

You built a robot? I can reasonably expect you to know something about electrical engineering and math.