# Objective
bevy_ecs has several compile_fail tests that assert lifetime safety. In the past, these tests have been green for the wrong reasons (see e.g. #2984). This PR makes sure, that they will fail if the compiler error changes.
## Solution
Use [trybuild](https://crates.io/crates/trybuild) to assert the compiler errors.
The UI tests are in a separate crate that is not part of the Bevy workspace. This is to ensure that they do not break Bevy's crater builds. The tests get executed by the CI workflow on the stable toolchain.
