Memory leak with `fetch` on Node v19+ when using Jest's `--detectLeaks`

[enisdenjo]

Version

Node >=v19

Steps to reproduce

1. Clone enisdenjo/jest-fetch-leak repo
2. Read its readme for local repro
3. Check out the GitHub Actions for CI repo

Expected behavior

Doesn't leak ever.

Actual behavior

Leaks in Node >=v19 when test is repeated enough times.

Additional context

⚠️ Not really sure whether this issue belongs here or on Jest's repo. But, I have a hunch that it belongs here given that we're experiencing memory spikes with Node >=v19 in production. Nevertheless, I've opened an issue there too.

If a test, which uses native fetch, is iterated enough times in Node >=v19, Jest's --detectLeaks will report a memory leak.

This behaviour does not happen on Node <=v18.

Please check the leak detector tests in the CI.

Environment

ubuntu-latest from GitHub Actions

[bnoordhuis]

When you say "memory leak", you mean this, right?

    EXPERIMENTAL FEATURE!
    Your test suite is leaking memory. Please ensure all references are cleaned.

    There is a number of things that can leak memory:
      - Async operations that have not finished (e.g. fs.readFile).
      - Timers not properly mocked (e.g. setInterval, setTimeout).
      - Keeping references to the global scope.

      at onResult (node_modules/@jest/core/build/TestScheduler.js:150:18)
          at Array.map (<anonymous>)

Since that's a jest feature and I don't plan on investigating how it tracks that, you should either report it to jest (and have them circle back to us if it turns out it's a node issue) or demonstrate the leak without using third-party modules.

[bnoordhuis]

I'll close this for now but let me know when there is reason to reopen.