Testing with temorary directory passed in a thread-local variable

---

examples/testing/tempfile-with-thread-local/Cargo.toml

[package]
name = "tempfile-with-thread-local"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
rand = "0.8.5"
tempfile = "3.9.0"

examples/testing/tempfile-with-thread-local/src/main.rs

use std::fs::File;
use std::io::Write;

use std::cell::RefCell;

thread_local! {
    pub static RESULT_PATH: RefCell<String> = const { RefCell::new(String::new()) };
}

fn main() {}

#[allow(dead_code)]
fn add(x: i32, y: i32) -> i32 {
    let time: u64 = rand::random();
    let time = time % 3;

    std::thread::sleep(std::time::Duration::from_secs(time));

    RESULT_PATH.with_borrow(|file_path| {
        let mut file = File::create(file_path).unwrap();
        println!("add({x}, {y}) file {file_path}");
        writeln!(&mut file, "{}", x + y).unwrap();
    });
    x + y
}

#[test]
fn test_add_2_3_5() {
    println!("{:?}", std::thread::current().id());
    let tmp_dir = tempfile::tempdir().unwrap();
    println!("tmp_dir: {:?}", tmp_dir);
    let file_path = tmp_dir.path().join("result.txt");
    println!("2+3 - file_path {:?}", file_path);
    let result_path = file_path.as_os_str().to_str().unwrap();
    RESULT_PATH.with_borrow_mut(|v| v.push_str(result_path));

    let result = add(2, 3);
    assert_eq!(result, 5);

    let result = std::fs::read_to_string(file_path).unwrap();
    assert_eq!(result, "5\n");
}

#[test]
fn test_add_4_4_8() {
    println!("{:?}", std::thread::current().id());

    let tmp_dir = tempfile::tempdir().unwrap();
    println!("tmp_dir: {:?}", tmp_dir);
    let file_path = tmp_dir.path().join("result.txt");
    println!("4+4 - file_path {:?}", file_path);
    let result_path = file_path.as_os_str().to_str().unwrap();
    RESULT_PATH.with_borrow_mut(|v| v.push_str(result_path));

    let result = add(4, 4);
    assert_eq!(result, 8);

    let result = std::fs::read_to_string(file_path).unwrap();
    assert_eq!(result, "8\n");
}