Testing the value of promises in Javascript without using Promise

Source: https://stackoverflow.com/a/54029876/4456532

Use case: when testing a code in Jest that already uses promises, I didn't want to use Promise resolve to peek into the promise, in order to not mess up the function execution. 

My helper function:

function promiseValue(p) {
	return process.binding('util').getPromiseDetails(p)[1];
}

Test for it with Jest:

test('promiseValue', () => {
	expect(promiseValue(new Promise(()=>{}))).toEqual(undefined);
	expect(promiseValue(Promise.resolve(2))).toEqual(2);
	expect(promiseValue(Promise.reject(0))).toEqual(0);
})