I don't agree. One part of coding tests is getting the right output, the other part is how they went about it - which is relevent even if they didn't solve the problem. You can tell a lot from the second part.
I'm not a huge fan of coding tests, and I have a lot of sympathy for those who refuse to do them, but it's a case of "It's not you, it's everyone else"
I believe it to be much better to see a candidate write some code quickly, have them write unit tests for it, discover that some cases were not handled properly and then they were.
This is how 99% of developers work, I don't believe anyone who says they write their code perfectly and under stress every single time.
I'm not a huge fan of coding tests, and I have a lot of sympathy for those who refuse to do them, but it's a case of "It's not you, it's everyone else"