Maybe I'm misunderstanding you, but it sounds like you mean that you trust it to produce that error when it's running (ie. in production). If that's the case, couldn't you do the same for all kinds of bugs and not bother writing tests at all? Put another way, what is different from this class of bug, which you don't think is worth testing, and other classes of bugs, which it sounds like you do?

Primarily specificity.

I want the function to fail when it is passed the wrong arguments, but I don't really care about how exactly it fails. If the wrong types get passed to a function, I'm already screwed and there's no way to do the right thing at that point. I only care that I get enough information to debug what happened.

In pretty much any other case, I want to function return some precise value or do some precise action. These are situations that the code will encounter during normal execution, and so I do care about what exactly it does.