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: watch.rs
    path of file: ./repos/leptos/leptos_reactive/tests
    
    the code of the file until where you have to start completion: use leptos_reactive::{
    create_runtime, create_signal, watch, SignalGet, SignalSet,
};
use std::{cell::RefCell, rc::Rc};

#[test]
fn watch_runs() {
    let runtime = create_runtime();

    let (a, set_a) = create_signal(-1);

    // simulate an arbitrary side effect
    let b = Rc::new(RefCell::new(String::new()));

    let stop = watch(
        move || a.get(),
        {
            let b = b.clone();

            move |a, prev_a, prev_ret| {
                let formatted = format!(
                    "Value is {}; Prev is {:?}; Prev return
    
fn watch_ignores_callback() {
    let runtime = create_runtime();

    let (a, set_a) = create_signal(-1);
    let (b, set_b) = create_signal(0);

    // simulate an arbitrary side effect
    let s = Rc::new(RefCell::new(String::new()));

    let _ = watch(
        move || a.get(),
        {
            let s = s.clone();

            move |a, _, _| {
                let formatted =
                    format!("Value a is {}; Value b is {}", a, b.get());
                *s.borrow_mut() = formatted;
            }
        },
        false,
    );

    set_a.set(1);

    assert_eq!(s.borrow().as_str(), "Value a is 1; Value b is 0");

    *s.borrow_mut() = "nothing happened".to_string();

    set_b.set(10);

    assert_eq!(s.borrow().as_str(), "nothing happened");

    set_a.set(2);

    assert_eq!(s.borrow().as_str(), "Value a is 2; Value b is 10");

    runtime.dispose();
}