Playwright could not find tests with Nextjs 15 experimental testmode

[KagamiChan]

Link to the code that reproduces this issue

https://github.com/KagamiChan/next15-playwright-test-not-found

To Reproduce

1. run npm run build
2. run npx playwright test
3. playwright reports "No tests found"

next15-playwright-test-not-found> npx playwright test
Error: No tests found

To open last HTML report run:

  npx playwright show-report

Current vs. Expected behavior

playwright should detect the test cases and run it.

Provide environment information

Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 11 Pro
  Available memory (MB): 64618
  Available CPU cores: 32
Binaries:
  Node: 21.7.1
  npm: N/A
  Yarn: N/A
  pnpm: N/A
Relevant Packages:
  next: 15.0.1 // Latest available version is detected (15.0.1).
  eslint-config-next: 15.0.1
  react: 19.0.0-rc-69d4b800-20241021
  react-dom: 19.0.0-rc-69d4b800-20241021
  typescript: 5.6.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

Testing

Which stage(s) are affected? (Select all that apply)

next start (local)

Additional context

I also tried with pnpm and the result is the same, so it might not be an issue of package manager

The setup is following the instructions here: https://github.com/vercel/next.js/blob/canary/packages/next/src/experimental/testmode/playwright/README.md

This used to work with v14