#[cfg(test)]

mod tests {

    #[test]

    fn test() {
        #[derive(Debug)]

        struct Data {
            value: usize,
        }

        impl Data {
            fn mut_value(&mut self) -> &mut usize {
                &mut self.value
            }
        }

        let mut data = Data { value: 0 };

        *data.mut_value() += 1;

        println!("{:?}", data);
    }
}