Asynchronous Systems

Testing Asynchronous Behavior with Eventual Assertions

Testing Asynchronous Behavior with Eventual Assertions A test starts background work and then checks the result. On a fast machine the work finishes first and the test passes. Under CI load, the assertion runs a few milliseconds earlier and fails. Someone adds sleep(1 second). The failure disappears, but every successful run now pays a full second, and a sufficiently slow run can still fail. The problem is not that the test needs a longer delay. The test doesn’t know exactly when the result will become observable.