The absolute limits of terms of service aren't clear, but there have been tons of cases about website/software terms of service. A quick search of Westlaw finds hundreds of reported cases in my state alone. There are certain things like binding arbitration that courts have found unconscionable to be in a clickwrap agreement[0], but generally terms of service have been found fully enforceable. There's definitely been a lot of court testing.[1]
I assume you mean US courts? In other countries there have been lots of cases about TOS, in one way or another. Strange that there isn't such a thing in the us
Not the parent commenter nor a lawyer, but I believe it's something like a company can't put things that someone would never agree to in the TOS and have it be binding. But obviously that "would never agree to" part is fuzzy at best and possibly what they're referring to when saying it's not been tested. I might be mistaken about that but I have heard something to that effect from a prosecutor I know.
[0]: https://www.faegredrinker.com/en/insights/publications/2022/...
[1]: https://www.goodwinlaw.com/en/insights/publications/2022/08/...