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Mastering Time: Using Fake Timers with Vitest
Level Up Your Timers Tests With Speed and Isolation
In the world of testing, controlling time can be a real challenge. Real-world timers, like setTimeout() and setInterval(), can be cumbersome when writing unit tests: without the right technique, you will introduce external dependencies on actual time passing that will make your test either slower, wrong or difficult to understand.
This is where Vitest’s fake timers come in, giving you the power to manipulate time within your tests for a smoother and more efficient testing experience.
At PlayPlay, we create high-quality software while prioritizing efficient development practices. We leverage innovative tools like Vitest’s fake timers to write faster and more reliable tests, ensuring exceptional software from the ground up.
Why Fake Timers?
Imagine testing a function that debounces another one after a 2-second delay. Using real timers, your test would have to wait for the full 2 seconds to pass, making the whole test scenario longer by these 2 seconds. This is slow and inefficient, and even more when you’re dealing with multiple timers or complex timing interactions. Hopefully, fake timers are here to allow you to:
- Speed up tests: Advance the virtual clock by any amount, making tests run significantly faster. This is particularly beneficial for tests that involve waiting for timers to expire or simulating longer time intervals. Vitest prioritizes test speed. Fake timers become even more crucial when dealing with functions that rely on timers. You can avoid waiting for long intervals, keeping your tests lightning fast.
- Isolate functionality: By removing reliance on external timers, you ensure your tests focus solely on the code you’re testing. This eliminates external factors that could potentially cause flaky tests and makes it easier to pinpoint the source of any issues.
- Simulate specific timeouts: Test how your code behaves under different time constraints. Fake timers allow you to create scenarios with specific delays or timeouts, helping you ensure your code functions as expected in various situations. You can check something’s state just before the timer is executed and…
