Catching MochaJS timeouts - mocha.js

Question

This question has been asked before, but the answer given was to re-write the specific code that was used in that case.
The Mocha documentation only mentions changing the duration of timeouts, and not the behaviour on timeout.
In my case, I want to test code that under certain conditions does not have any side effects. The obvious way to do this is to call the code, wait for Mocha to time out, and then run some assertions on my spies, e.g.:
this.onTimeout(function() {
assert.equal(someObject.spiedMethod.called, false);
});
someAsyncFunction();
Is this possible, or do I have to resort to setting my own timeout, e.g.:
// 1. Disable the mocha timeout
this.timeout(0);
// 2. create my own timeout, which should fire before the mocha timeout
setTimeout(function() {
assert.equal(someObject.spiedMethod.called, false);
done();
}, 2000);
someAsyncFunction();

Answer 1

Mocha's own timeouts are designed only to detect when tests are considered to be slow beyond anything reasonable. An asynchronous computation could be buggy in such a way that causes it to never terminate. Rather than wait forever, Mocha lets you decide that after X time it should fail the test. As soon as the timeout is hit, Mocha gives up on the test that timed out.
So you have to set your own timeouts.

Answer 2

Was facing a similar problem & also didn't find a way to do that in mochajs.
However, if you want to run some code on test timeout, you could structure your code like this:
describe('something', function() {
const TEST_TIMEOUT = 10000
this.timeout(TEST_TIMEOUT)
beforeEach('set timeout callback', function() {
setTimeout(function() {console.log('hi')}, TEST_TIMEOUT)
})
})
A few caveats:
1- I'm not sure if it'd affect a test's result. But if it were to, I'd setTimeout with TEST_TIMEOUT minus some time to make sure my assertions run before the mochajs timeout fires.
2- On the contrary, if the goal of the callback is not to do some assertions but to run some code (e.g., cleanup or logging), I'd set the timeout to be TEST_TIMEOUT plus some time.
Starting with mocha v4 (or with --no-exit flag in previous versions), as long as you have a timeout (or other handlers/the process didn't terminate), mocha will not force exit as it used to, so you can be comfortable your code will run.