Well I certainly wouldn’t consider random online tests and quizzes to be any kind of serious measurement of anything.

Yes real testing has its validity. Absolutely. In conjunction with other means and observations.

We do need proper IQ testing (in conjunction with other measures and no, not online quizzes) to determine cognitive impairment. You can’t distegard testing completely

I don’t want doctors who can’t pass board exams to operate on me. Yes test taking is a skill, and it’s a valid skill. It could determine how fast one can make decisions and if one can think logically and if one can do more than just memorize etc

Now of course we aren’t talking about some random online quizzes.

And of course not all test results are equally valid or accurate. And there are many factors to consider. If you are trilingual, what language should you be tested in? Native? What if you mostly speak your third language, which isn’t even near being native but that’s the one you mostly use? What if you have Tourette’s and tick with your hand so bad it slows down your responses and you can’t finish test on time? What if you have ASD and simply don’t want to answer some questions? Your IQ test won’t be accurate. That’s why we need other measures

But we can’t really argue that tests have no validity. It’s just not realistic.