Testing

Rust community typically authors unit tests in a module placed in the same source file as the code being tested. This was covered earlier in the course and looks like this:

#![allow(unused)]
fn main() {
#[cfg(test)]
mod tests {
    #[test]
    fn my_test() {
        todo!()
    }
}
}

In Chromium we place unit tests in a separate source file and we continue to follow this practice for Rust — this makes tests consistently discoverable and helps to avoid rebuilding .rs files a second time (in the test configuration).

This results in the following options for testing Rust code in Chromium:

• Native Rust tests (i.e. #[test]). Discouraged outside of //third_party/rust.
• gtest tests authored in C++ and exercising Rust via FFI calls. Sufficient when Rust code is just a thin FFI layer and the existing unit tests provide sufficient coverage for the feature.
• gtest tests authored in Rust and using the crate under test through its public API (using pub mod for_testing { ... } if needed). This is the subject of the next few slides.