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: mod.rs
    path of file: ./repos/hash/libs/@blockprotocol/type-system/rust/src/ontology/data_type
    
    the code of the file until where you have to start completion: use std::{collections::HashMap, ptr};

pub use error::ParseDat
    
    fn validate_data_type_ref_invalid() {
        let url_a =
            VersionedUrl::from_str("https://blockprotocol.org/@alice/types/property-type/age/v/2")
                .expect("failed to parse VersionedUrl");
        let url_b =
            VersionedUrl::from_str("https://blockprotocol.org/@alice/types/property-type/name/v/1")
                .expect("failed to parse VersionedUrl");

        let data_type_ref = DataTypeReference::new(url_a);

        data_type_ref
            .validate_url(&url_b.base_url)
            .expect_err("expected validation against base URL to fail but it didn't");
    }