How to: ⚪ ️ 3.4 Don't sleep, use frameworks built-in support for async events. Also try to speed things up
:white_check_mark: **Do:** In many cases, the unit under test completion time is just unknown (e.g. animation suspends element appearance) - in that case, avoid sleeping (e.g. setTimeOut) and prefer more deterministic methods that most platforms provide. Some libraries allows awaiting on operations (e.g. [Cypress cy.request('url')](https://docs.cypress.io/guides/references/best-practices.html#Unnecessary-Waiting)), other provide API for waiting like [@testing-library/dom method wait(expect(element))](https://testing-library.com/docs/guide-disappearance). Sometimes a more elegant way is to stub the slow resource, like API for example, and then once the response moment becomes deterministic the component can be explicitly re-rendered. When depending upon some external component that sleeps, it might turn useful to [hurry-up the clock](https://jestjs.io/docs/en/timer-mocks). Sleeping is a pattern to avoid because it forces your test to be slow or risky (when waiting for a too short period). Whenever sleeping and polling is inevitable and there's no support from the testing framework, some npm libraries like [wait-for-expect](https://www.npmjs.com/package/wait-for-expect) can help with a semi-deterministic solution
❌ **Otherwise:** When sleeping for a long time, tests will be an order of magnitude slower. When trying to sleep for small numbers, test will fail when the unit under test didn't respond in a timely fashion. So it boils down to a trade-off between flakiness and bad performance
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Code Examples