#[cfg(test)] doesn't work in dependencies

[tye-exe]

When running the unit test for a crate, the #[cfg(test)] attribute is not respected for dependencies, & the dependent crate cannot use code that is gated behind this condition.
I am not sure as to whether this is a bug or an intended feature and I cannot find documentation in regards to either.

For a minimum reproducible example see my repository.
For an in-line example:

// In crate `conditional`
#[cfg(test)]
pub struct Contitional;

// Separate crate depending on `conditional`
#[cfg(test)]
mod tests {

    #[test]
    fn use_contitional() {
        conditional::Conditional;
    }
}

Gives the following error when cargo test is run:

error[E0425]: cannot find value `Conditional` in crate `conditional`

Notes

I found this issue on the rust repository, which suggested to open an issue on the cargo repository, but i was not able to find such an issue, so i am opening one myself.

Cargo version information

cargo 1.87.0-nightly (6cf826701 2025-03-14)
release: 1.87.0-nightly
commit-hash: 6cf8267012570f63d6b86e85a2ae5627de52df9e
commit-date: 2025-03-14
host: x86_64-unknown-linux-gnu
libgit2: 1.9.0 (sys:0.20.0 vendored)
libcurl: 8.12.1-DEV (sys:0.4.80+curl-8.12.1 vendored ssl:OpenSSL/3.4.1)
ssl: OpenSSL 3.4.1 11 Feb 2025
os: NixOS 24.11.0 [64-bit]

[epage]

This appears to be a duplicate #8379 and closing in favor of that. If there is a reason for us to keep this open separately, let us know!