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Performance loss between jest 25.1.0 and 25.2.7

See original GitHub issue

💥 Regression Report

We run about 7000 tests total across 630 test files without coverage (see https://github.com/facebook/jest/issues/9457). On my machine, with 25.1.0, the tests took 140 seconds, compared to 350 seconds with 25.2.7. I am running Windows, I believe the effect is less noticeable (but still there) on mac/linux.

Last working version

Worked up to version: 25.1.0

Stopped working in version: somewhere between 25.1.0 and 25.2.7

To Reproduce

Steps to reproduce the behavior: Update from jest 25.1.0 to 25.2.7

Expected behavior

Test run time should not increase drastically when upgrading versions.

Link to repl or repo (highly encouraged)

I don’t have a publicly available repo to show, but here are some performance charts I captured. I’m not familiar with the inner workings of Jest, but it appears the performance regression probably has something to do with the resolution of symlinks? We’re not using any symlinks as far as I am aware. 25.1.0: performance_before 25.2.7: performance_after

Run `npx envinfo --preset jest`

System: OS: Windows 10 10.0.14393 CPU: (12) x64 Intel® Core™ i7-8850H CPU @ 2.60GHz Binaries: Node: 12.14.0 - C:\Program Files\nodejs\node.EXE npm: 6.14.4 - C:\Users*****\AppData\Roaming\npm\npm.CMD npmPackages: jest: 25.2.7 => 25.2.7