warning: unknown lint: `test_unstable_lint`
  --> $DIR/feature-gate-test_unstable_lint.rs:4:1
   |
LL | #![allow(test_unstable_lint)]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: the `test_unstable_lint` lint is unstable
   = help: add `#![feature(test_unstable_lint)]` to the crate attributes to enable
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
   = note: `#[warn(unknown_lints)]` on by default

warning: 1 warning emitted