Use modern timers in monorepo Jest tests#38955
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Summary: Pull Request resolved: facebook#38955 Jest introduced "modern" timers based on `sinon/fake-timers` in Jest 26 ([release announcement](https://jestjs.io/blog/2020/05/05/jest-26#new-fake-timers)), and they became the default in Jest 27, in May 2021. Modern timers have more capabilities - they were introduced with support for `queueMicrotask`, mocking `Date`, etc., and they've continued to receive more attention from the Jest team since - they're now much more comprehensive and more configurable than legacy timers. Importantly, because they're not based on Jest mocks, they're not affected in surprising ways by eg `jest.resetAllMocks()` (a particularly confusing side-effect when fake timers are enabled globally, as in our setup). This migrates RN's own tests and config to modern fake timers, or real timers where that's more appropriate. NOTE: In cases where non-trivial changes to the tests are required, four test files are individually opted-in to `legacyFakeTimers` with a `TODO(legacy-fake-timers)`. I'll open these up for community contributions to fix. Changelog: [Internal] Reviewed By: motiz88 Differential Revision: D48189907 fbshipit-source-id: f5eea9a1880cbf98070e09b7639045d412bc11c3
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Summary:
Jest introduced "modern" timers based on
sinon/fake-timersin Jest 26 (release announcement), and they became the default in Jest 27, in May 2021.Modern timers have more capabilities - they were introduced with support for
queueMicrotask, mockingDate, etc., and they've continued to receive more attention from the Jest team since - they're now much more comprehensive and more configurable than legacy timers.Importantly, because they're not based on Jest mocks, they're not affected in surprising ways by eg
jest.resetAllMocks()(a particularly confusing side-effect when fake timers are enabled globally, as in our setup).This migrates RN's own tests and config to modern fake timers, or real timers where that's more appropriate.
NOTE: In cases where non-trivial changes to the tests are required, four test files are individually opted-in to
legacyFakeTimerswith aTODO(legacy-fake-timers). I'll open these up for community contributions to fix.Changelog: [Internal]
Differential Revision: D48189907