circular_buffer: Shall we remove `allow(unused_must_use)`?

[petertseng]

You will observe that https://github.com/exercism/rust/blob/master/exercises/circular-buffer/tests/circular-buffer.rs contains an allow(unused_must_use) to avoid compiler warnings (and thus a CI rejection, since our CI rejects warnings) from the fact that many Results from write are ignored.

Shall we instead use let _ = buffer.write(...) ?

The advantage is that it is more precise about exactly which lines are ignoring a Result rather than casting a wide net over the entire test module.

It would also allow us to remove an mod tests that is present in only circular-buffer probably for the sole reason of scoping the #[allow(...)]

The disadvantage is that since there may be other reasons to use let _ = ... it makes it hard to grep the entire repo to determine what's ignoring a Result and what is using let _ = ... for other reasons.

The circular-buffer was added in #52 at which time there was no discussion of this point.

The other exercise that prominently uses let _ = ... is Bowling; the discussion may be seen around #213 (comment) and a few surrounding comments (such as #213 (comment))

[petertseng]

Of course, we may also decide to use something like expect or assert_eq!(Ok(...), buffer.write(...) if we want to assert on the write; it would certainly provide feedback faster.

[coriolinus]

I think that expect is probably the best solution here, possibly with an explanatory comment to the effect of we know this will succeed because we have perfect control of the test environment. expect is still not recommended for production code! at the first instance. It's explicit and gets across the point that this isn't what the tests are intended to measure.