rustdoc book doesn't mention assert in doc tests

[steveklabnik]

this is non-obvious to some people, we should add it.

[GuillaumeGomez]

It's a macro and you're supposed to be able to write any rust code you want, so how can it be non-obvious? :-/ I'm a bit skeptical about this one (not against, just surprised).

[steveklabnik]

I got more than one question about it, basically.

[Songbird0]

So should we add it? We could simply add a line indicating that macros dedicated to assertions can also be used into the documentation.

This would be a simple clarification for Rust learners.

cc @GuillaumeGomez @steveklabnik

[steveklabnik]

Yeah, we should, IMO.

[GuillaumeGomez]

We should indeed.

[Songbird0]

All right! I'll submit some changes.

[frewsxcv]

as per #48961, this is now done 🎉

https://doc.rust-lang.org/nightly/rustdoc/documentation-tests.html#passing-or-failing-a-doctest

thanks @Songbird0!