Relies on internals of Cargo and will break with existing / upcoming features

[epage]

Tests assumes the location of build artifacts

• This isn't the case if we approve the new build-dir layout (Re-organize build-dir by package + hash, rather than artifact type rust-lang/cargo#15010)

You can reproduce this by running:

$ cargo +nightly test -Zbuild-dir-new-layout

This problem was identified by the following crater run: rust-lang/rust#149852