warning: unknown lint: `test_unstable_lint`
   |
   = note: the `test_unstable_lint` lint is unstable
   = help: add `#![feature(test_unstable_lint)]` to the crate attributes to enable
   = note: requested on the command line with `-W unknown-lints`

warning: unknown lint: `test_unstable_lint`
   |
   = note: the `test_unstable_lint` lint is unstable
   = help: add `#![feature(test_unstable_lint)]` to the crate attributes to enable

warning: unknown lint: `test_unstable_lint`
   |
   = note: the `test_unstable_lint` lint is unstable
   = help: add `#![feature(test_unstable_lint)]` to the crate attributes to enable

warning: 3 warnings emitted