trpl-zh-cn/listings/ch11-writing-automated-tests/no-listing-04-bug-in-add-two/src/lib.rs

// ANCHOR: here
pub fn add_two(a: usize) -> usize {
    a + 3
}
// ANCHOR_END: here

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn it_adds_two() {
        let result = add_two(2);
        assert_eq!(result, 4);
    }
}