Retryable assertions

When testing asynchronous code, your system often arrives at the expected state eventually. That is why you often express your intentions in tests as "wait for X to happen" instead of claiming "X must happen immediately".

In Promise-based APIs, that expectation is neatly abstracted behind the async/await keywords to keep your tests clean:

const response = await fetch('/api/songs')
await expect(response.json()).resolves.toEqual(favoriteSongs)

While fetching the list of songs takes time, that eventuality is represented as a Promise that you can await. This guaratees that your test will not continue until the data is fetched. Quite the same applies to reading the response body stream.

But not all systems are designed like that. And even the systems that are designed like that may not expose you the right Promises to await.

In those situations, you likely reach to utilities like waitFor() to help you express the expected eventual state of your tested code.

api.sideEffect()

await vi.waitFor(() => {
	expect(api.state).toEqual(expectedState)
})

And this works great. But today, I'd like to show you a different approach to expressing eventual expectations.

Your task

👨‍💼 In

src/client.test.ts

, a new challenge is waiting for you. Follow the instructions to replace vi.waitFor() with a new API called expect.poll(). Make sure your tests are passing once you're done, and see you soon!

03. Assertions/04. Retryable assertions (💪 problem)

Retryable assertions

Your task