You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: anamorphism_example.rs
    path of file: ./repos/fp-core.rs/fp-examples/src
    
    the code of the file until where you have to start completion: #[cfg(test)]
mod example {
    
    
    fn anamorphism_example() {
        let count_down = unfold((8_u32, 1_u32), |state| {
            let (ref mut x1, ref mut x2) = *state;

            if *x1 == 0 {
                return None;
            }

            let next = *x1 - *x2;
            let ret = *x1;
            *x1 = next;

            Some(ret)
        });

        assert_eq!(
            count_down.collect::<Vec<u32>>(),
            vec![8, 7, 6, 5, 4, 3, 2, 1],
        );
    }