unit testing collection exploration on rust

lib.rs

#[cfg(test)]
mod string_manipulation {
    #[test]
    fn appending_string_literal() {
        let mut s = String::from("foo");
        s.push_str("bar");
        assert_eq!(s, "foobar");
    }

    #[test]
    fn appending_a_string() {
        let mut foo = String::from("foo");
        let bar = String::from("bar");

        // this is in immutable reference
        foo.push_str(&bar);

        assert_eq!(foo, "foobar");
    }

    #[test]
    fn appending_a_string_by_turning_it_into_a_string_literal() {
        let mut foo = String::from("foo");
        let bar = String::from("bar");

        foo.push_str(bar.as_str());

        assert_eq!(foo, "foobar");
    }

    #[test]
    fn adding_string_using_plus() {
        let foo = String::from("foo");
        let bar = String::from("bar");
        let foobar = foo + &bar;

        assert_eq!(foobar, "foobar");
    }

    #[test]
    fn multiple_addition() {
        let satu = String::from("satu");
        let dua = String::from("dua");
        let tiga = String::from("tiga");

        let semua = format!("{}-{}-{}", satu, dua, tiga);

        assert_eq!(semua, "satu-dua-tiga");
    }
}

#[cfg(test)]
mod hash_map {

    use std::collections::HashMap;

    #[test]
    fn adding_element() {
        let mut ibu_kota = HashMap::new();
        ibu_kota.insert("Jawa Timur", "Surabaya");
        ibu_kota.insert("Jawa Barat", "Bandung");

        assert_eq!(2, ibu_kota.len());
    }


    #[test]
    fn getting_value() {
        let mut ibu_kota = HashMap::new();
        ibu_kota.insert("Jawa Timur", "Surabaya");
        ibu_kota.insert("Jawa Barat", "Bandung");

        match ibu_kota.get(&"Jawa Timur") {
            Some(&province) => assert_eq!("Surabaya", province),
            _ => assert!(true, false),
        }
    }

    #[test]
    fn removing_an_element() {
        let mut ibu_kota = HashMap::new();
        ibu_kota.insert("Jawa Timur", "Surabaya");
        ibu_kota.insert("Jawa Barat", "Bandung");

        ibu_kota.remove(&"Jawa Timur");
        
        assert_eq!(1, ibu_kota.len());
    }
}