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[Bug]: Jest 27 - useFakeTimers erases performance.mark and friends

See original GitHub issue

Version

27.3.1

Steps to reproduce

window.performance.mark = () => {}
jest.useFakeTimers()
assert(typeof window.performance.mark === 'undefined')

jest.useRealTimers()
assert(typeof window.performance.mark === 'function')

jest.useFakeTimers("legacy")
assert(typeof window.performance.mark === 'function')

Expected behavior

jest.useFakeTimers() to not override global polyfills/mocks of performance.mark

Actual behavior

jest.useFakeTimers() overrides global polyfills/mocks of performance.mark, and sets it to undefined.

Additional context

I found a similar issue in @sinonjs/fake-timers https://github.com/sinonjs/fake-timers/issues/136. Don’t know if it’s related to jest though.

Environment

System:
    OS: macOS 12.0.1
    CPU: (10) arm64 Apple M1 Pro
Binaries:
    Node: 16.13.0 - /usr/local/bin/node
    Yarn: 3.0.0-rc.9 - /opt/homebrew/bin/yarn
    npm: 8.1.0 - /usr/local/bin/npm

Issue Analytics

State:
Created 2 years ago
Reactions:4
Comments:11 (3 by maintainers)

Top GitHub Comments

4reactions

vovacodescommented, Nov 10, 2021

The use-case is pretty straight-forward:

I have some code that does performance.mark() somewhere deeply in its implementation
I want to test some parts of this code and I don’t care about performance.mark() and I’m fine with it just being a noop.
I put a “global” stub for performance.mark() in my setupFile.js
I expect that performance.mark() always will be around so my tests don’t crash.

I’d be ok with any way of making it happen, even things like jest.useFakeTimers({ ignore: [window.performance] }) or whatever

2reactions

fatso83commented, Dec 23, 2021

I think this issue could be fixed pretty easily be just making avoiding to fake performance. This is already possible by telling @sinonjs/fake-timers, but we have just forgot to update our docs … 🙈 Ref https://github.com/sinonjs/fake-timers/issues/409, https://github.com/DefinitelyTyped/DefinitelyTyped/pull/56961#pullrequestreview-797296492 and https://github.com/sinonjs/fake-timers/issues/374.

@SimenB I am not to well versed in Jest’s use of fake timers, but I do not see any way of passing options to customise its timer faking. If we could exclude performance this issue would go away. p.s. Thanks for the ☕

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