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: vectree.rs
    path of file: ./repos/sorceress/src
    
    the code of the file until where you have to start completion: // Sorceress
// Copyright (C) 2021  Wesley Merkel
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General 
    
    fn iterator_test() {
        let empty: Vec<i32> = vec![];
        let empty_branch: VecTree<i32> = branch(&[]);
        assert_eq!(empty, to_vec(empty_branch));
        assert_eq!(vec![1], to_vec(leaf(1)));
        assert_eq!(vec![1], to_vec(branch(&[leaf(1)])));
        assert_eq!(vec![1, 2], to_vec(branch(&[leaf(1), leaf(2)])));
        assert_eq!(vec![1, 2], to_vec(branch(&[branch(&[leaf(1)]), leaf(2)])));
    }