Why `async/await` doesn't work in my case?

await only suspends when the value passed to it is a Promise. In your case, setTimeout returns a Number so await doesn't wait for it.

The correct code will be as follows:

async function test() {
    console.log('1');
    await new Promise((resolve, reject) => {
        setTimeout(() => {
            console.log('2');
            resolve()
        }, 0);
    });
    console.log('3');
}

Because setTimeout doesn't return a promise. await x only waits if x is a promise; if x isn't a promise, it's (effectively) wrapped in one as though you had await Promise.resolve(x). That means the code following it will run asynchronously but as soon as possible.*

If you want a promise version of setTimeout, see this question's answers. But even with that, your test function wouldn't use a callback, instead you'd just await the promise-enabled timeout:

function later(delay) {
    return new Promise(function(resolve) {
        setTimeout(resolve, delay);
    });
}

async function test() {
  console.log("1");
  await later(10);
  console.log("2");
  console.log("3");
}

test().catch(e => console.error(e));
console.log("After the call (just to prove it does wait for the timeout after 1 and before 2");

* On browsers, that's guaranteed to be before a setTimeout(..., 0) scheduled during the same task, because promise callbacks scheduled during a task occur just after the end of that task, before the next task is picked up from the queue (even if the next task was scheduled before the promise callback). More on this ("macrotasks" and "microtasks") in this question's answers.