Simplifies testing promise-returning-functions that executes timers (setTimeout / setInterval). The helper `runTimersUntilResolved` will run the timers repeatedly until the promise resolves. Jest helper.

jest-run-timers-until-resolved.ts

/*
 * Run timers (setInterval/setTimeout) every tick continuously until the promise has been resolved
 */
async function runTimersUntilResolved(fn: () => Promise<any>) {
  jest.useFakeTimers();

  let isResolved = false;
  const p = fn();
  p.finally(() => (isResolved = true));

  while (isResolved === false) {
    // tick
    await new Promise((resolve) => setImmediate(resolve));

    // run timers
    jest.runAllTimers();
  }

  return p;
}
  
// Example:
const res = await runTimersUntilResolved(() => myAsyncOperation())
expect(rest).toEqual('something');