[Bug]: Jest 30 seems to be 1.5x slower than v29

[bacarybruno]

Version

30.0.3

Steps to reproduce

• Clone the facebook/react repo
• Run yarn install
• Run the tests with yarn test
• Bump jest to v30.0.3
• Run the tests again

Expected behavior

According to the blogpost https://jestjs.io/blog/2025/06/04/jest-30, "Jest 30 is noticeably faster" than the previous versions.

Actual behavior

I attempted an upgrade on two private repositories and noticed that on both of them, jest 30 was slower.

Jest 29: Time: 57.615 s
Jest 30: Time: 90.925 s

Additional context

Environment

System:
    OS: macOS 15.5
    CPU: (12) arm64 Apple M4 Pro
  Binaries:
    Node: 20.19.0 - ~/.nvm/versions/node/v20.19.0/bin/node
    Yarn: 1.22.22 - ~/.nvm/versions/node/v20.19.0/bin/yarn
    npm: 10.8.2 - ~/.nvm/versions/node/v20.19.0/bin/npm
  npmPackages:
    jest: ^30.0.3 => 30.0.3

[Codexphere92]

My team is noticing the same thing

Jest 29: Time: ~130s
Jest 30: Time: ~170s

[tavvy]

Us too

Jest 29: ~97s
Jest 30: ~133s

[henriquekuwai]

Me too.

Jest 29: ~72s
Jest 30: ~125s

Ubuntu 24.04, 11th Gen Intel® Core™ i7-1165G7 × 8, 32GB RAM

[bacarybruno]

I did some investigating and found that the performance regression was introduced between 30.0.0-beta.3 and 30.0.0-beta.4.

Based on the diff v30.0.0-beta.3...v30.0.0-beta.4, it looks like this PR (feat(runtime): use compileFunction over new Script) could be the likely cause cc @SimenB (sorry for the wild ping 🙏).

I was also expecting some performance improvements from this PR, but it didn’t seem to have any noticeable impact on run durations 🤔 Is there anything to update on the config maybe to make it work?

[eyalroth]

Can anyone upload/link to a repo for reproducing this other than React?

I can't even seem to upgrade Jest in React's repo. I'm encountering this issue and many other errors. The setup in this repo is very complicated.

[bacarybruno]

Sorry I struggle to find a big open-source repo with significant test duration. On https://github.com/Shopify/polaris for example I had to use the --runInBand option to see a difference:

v29.7.0

v30.0.3

Without runInBand the difference was not that big (jest 29 was 2-3s slower).

[aclarembeau]

Observing the same issue here: RAM usage increased, and tests take way longer
Probably related to: nodejs/node#35375

[eyalroth]

On Shopify/polaris for example I had to use the --runInBand option to see a difference:

I'm assuming you were referring to the tests in polaris-react folder.

I got the same result with Node 20 (and running Jest 30 from my local clone of master, not the published version).

However, with Node 22, Jest 30 was faster (~25s) than both Jest versions in Node 20, while Jest 29 gotten worse (~35s).

What version of node are people here using in their projects that experience the slowdown?

[bacarybruno]

I'm assuming you were referring to the tests in polaris-react folder.

Yes 👍

What version of node

We are using Node 20 on our private repo

[aclarembeau]

We use node 22

[bacarybruno]

@eyalroth is there something else we can do to help? 🙏

[eyalroth]

@eyalroth is there something else we can do to help? 🙏

@bacarybruno I contributed a few major features in Jest 30, so I was interested to see if they may be the cause of this issue.

Unfortunately, I couldn't find any relation between my contributions and the issue.

This release was very big with many different contributions.