How to correctly spawn a server in thread?

[FMs-HanTetsusen]

Summary

I'm new to axum and currently writing a little project for practice.

My question is how do I spawn a server in a proper way for test cases?

pub fn app() -> Router {
    Router::new().route("/", get(root))
}

pub async fn listener() -> TcpListener {
    TcpListener::bind("127.0.0.1:3000").await.unwrap()
}


// This works (calling tokio::spawn in test)
let app = app();
let listener = listener().await;

tokio::spawn(async move { axum::serve(listener, app).await.unwrap() });


// But this fails (calling tokio::spawn in test)
async fn run() {
  let app = app();
  let listener = listener().await;

  axum::serve(listener, app).await.unwrap()
}

tokio::spawn(run());

I'm confused with the second case, why does it fail?
I'm trying to use the run() because in this way I can share code between the main fn and tests (i.e. keep app, listener, and axum::serve in a single fn, calling it from main fn, spawning it in test cases).

What is the proper way to do this?

axum version

0.7.5

[FMs-HanTetsusen]

I might have found the answer, I will try it later to see if this is the problem.

Tests: Wait until server has started? #1701