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: uuid.rs
    path of file: ./repos/artichoke/spinoso-securerandom/src
    
    the code of the file until where you have to start completion: //! Generator for Version 4 UUIDs.
//!
//! See [RFC 4122], Section 4.4.
//!
//! [RFC 4122]: https://tools.ietf.org/html/rfc4122#section-4.4

use rand::rngs::OsRng;
use rand::{CryptoRng, RngCore};
use scolapasta_hex as hex;

use crate::{Error
    
    fn test_v4_generated_uuids_are_unique() {
        let mut generated_uuids = HashSet::with_capacity(ITERATIONS);

        for _ in 0..ITERATIONS {
            let uuid = v4().unwrap();

            // Ensure uniqueness of generated UUIDs
            assert!(
                generated_uuids.insert(uuid.clone()),
                "Generated UUID is not unique: {uuid}"
            );
        }
    }