cargo test

running 1 test
test src/lib.rs - foo (line 1) ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out

lib.rs

/// ```rust
/// extern crate rayon;
/// ```
pub fn foo() {}

#[cfg(test)]
mod tests {
    #[test]
    fn it_works() {
        assert_eq!(2 + 2, 4);
    }
}