Testing for a very simple Rust API

main.rs

#[cfg(test)]
mod tests {
    use super::*;
    use actix_web::body::to_bytes;
    use actix_web::dev::Service;
    use actix_web::{http, test, web, App, Error};

    #[actix_web::test]
    async fn test_say_hello() -> Result<(), Error> {
        let app = App::new().route("/", web::get().to(say_hello));
        let app = test::init_service(app).await;

        let req = test::TestRequest::get().uri("/").to_request();
        let resp = app.call(req).await.unwrap();

        assert_eq!(resp.status(), http::StatusCode::OK);

        let response_body = resp.into_body();
        assert_eq!(to_bytes(response_body).await.unwrap(), r##"Hello world!"##);

        Ok(())
    }
}