Promise.reject + setTimeout causes UnhandledPromiseRejection error

Why this is a good first issue

Test fails due to unhandled promise rejection timing issue.

AI Summary

The issue involves a test failing due to promise rejection timing with setTimeout. The behavior suggests an async timing problem in test execution. While the reproduction is clear, the fix may require understanding Node.js's promise rejection handling internals.

Issue Description

Version

v25.0.0

Platform

Linux Federation 6.17.0-19-generic #19~24.04.2-Ubuntu SMP PREEMPT_DYNAMIC Fri Mar  6 23:08:46 UTC 2 x86_64 x86_64 x86_64 GNU/Linux

Subsystem

promises + timeouts

What steps will reproduce the bug?

The following test always fails:

./Trivial.js

"use strict";

// Happens with `const { setTimeout } = require("node:timers/promises");`, too
const setTimeout = (t) => new Promise((resolve) => globalThis.setTimeout(resolve, t));

async function main() {
  const badPromise = Promise.reject("bad value");
  console.debug("Promise created");
  await setTimeout(100);
  console.debug("Timeout awaited");
  try {
    console.debug("Awaiting promise");
    await badPromise;
    throw new Error("should not resolve");
  } catch (error) {
    console.debug("Task failed successfully:", error);
  }
};
main();

How often does it reproduce? Is there a required condition?

Every time.

What is the expected behavior? Why is that the expected behavior?

The trivial test should pass.

What do you see instead?

Trivial test runs fully, but reports as having failed before its execution ends, despite the rejected promise being awaited within a try/catch block.

output:

Fordi@the-laptop:~/develop/trivial-failure$ node --test Trivial.cjs
Promise created
node:internal/process/promises:330
      new UnhandledPromiseRejection(reason);
      ^

UnhandledPromiseRejection: This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason "bad value".
    at throwUnhandledRejectionsMode (node:internal/process/promises:330:7)
    at processPromiseRejections (node:internal/process/promises:413:17)
    at process.processTicksAndRejections (node:internal/process/task_queues:104:32) {
  code: 'ERR_UNHANDLED_REJECTION'
}

Node.js v25.0.0

Additional information

This situation i

GitHub Labels

timers