Run background task inside Jest - node.js

Question

I was writing an automatic test framework with Jest. For this, I need to run some background tasks under certain intervals. In summary, this is like polling. Let's give an example with a pseudo code.
test('Some potato poteto test', () => {
jest.setTimeout(12000000); // 20 min
const intervalPeriod = 5 * 60 * 1000; // 5 min
let retry = 0;
const intervalId = setInterval(() => {
console.log("I am doing my 5 minutes check");
// my custom logic goes here
retry++;
if(retry === MAX_RETRY) { // this will be always hit
clearInterval(intervalId)
}
}, intervalPeriod);
});
So, in every 5 mins, I'll make a network call, do some of my custom logic. Now, the problem is while running this, the test finished but jest can't terminate.
By 'test-finished' I meant, test suite ran, but the code inside the setInterval does not get executed right then.
My question is, does this happen because setInterval does not run immediately in the event-loop and is jest not configured to run a setInterval?
Please note that I don't want to mock the setInterval and also I don't want to use any fake timer.
Therefore, is it possible to achieve this with Jest?
I also tried the same thing with the cron library for node but it is the same issue. Jest does not execute the code and finish executing then halted because those setInterval/cron are still running in the background.
Is there a way to run those tasks inside Jest? I mean is there a way to run those jobs and when they are done then terminate Jest?

Answer 1

That's intended, Jest execute all the test instructions and quit the test.
For jest to wait for a computation, you need to use Promises and its async mode.
Doc for Jest async mode: https://jestjs.io/docs/asynchronous
Learn more about Promises here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise
And async/await syntax here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function
This is a naive way for doing it:
const MAX_RETRY = 3;
const INTERVAL_PERIOD = 5 * 60 * 1000; // 5 min
const SAFETY_TIME = INTERVAL_PERIOD;
const TEST_TIMEOUT = (1 + MAX_RETRY) * INTERVAL_PERIOD + SAFETY_TIME;
test('Some potato poteto test', async () => {
let retry = 0;
let success = false;
function yourLogicFunction(): boolean {
const resultOfYourLogicFunction = retry === MAX_RETRY; // because retry is used in this condition I store the result before changing it
console.log(`this is my attempt number ${retry}`);
retry++;
return resultOfYourLogicFunction;
}
function mockRequest(resolve: (value: unknown) => void): void {
setTimeout(() => resolve(yourLogicFunction()), INTERVAL_PERIOD);
}
while (!success && retry <= MAX_RETRY) {
success = await new Promise(mockRequest) as boolean;
}
}, TEST_TIMEOUT);
The third parameter of test is its timeout.