If you're in overtime, if the cache has expired, then the test expectation must change from ->get('test') returns 1 to ->get('test') returns nothing

As I already said, this will make test to pass, but same effect will be from ok(1) because this test won't test things it's supposed to test in this case.

Failing the test because you're in overtime is a poorly written test.

Agreed, this is why I've posted this question.

But I now see the real problem, you're using EV to implement expiration, but that is something every caching module ( Cache/CHI .. ) knows how to do without an event loop; in short, the module has no use case

Modules which implement this without EV have to either lose noticeable amount of performance for cache housekeeping on each $cache->get() and $cache->set(), or require user to don't forget to manually call $cache->housekeeping() every few seconds (which usually mean adding this operation into many different places of code to guarantee it will be called often enough).

In event-based applications we can avoid both performance loss and chaos in code by simply using EV->timer to call housekeeping code internally in module. This is the use case for this module.