hmm, doesn't work on windows in my testing. looking more.

Found the culprit! The real root cause is microsoft/playwright#9193. It still exists, but is hard to solve on Playwright's side. We can work around it by normalising the cwd we use spawn the test-server in, and that's what f311510 does.

I'll summarize the behaviour we're working around here for future visitors.

The Windows Filesystem is case-insensitive, but Node.js module loading is case-sensitive. That means that on Windows, C:\foo and c:\foo point to the same file, but on Node.js require-ing both of them will result in two instances of the file. This can lead to two instances of @playwright/test being loaded, which can't happen.

You can trigger this behaviour by running npx playwright test C:\tests\foo.spec.js c:\tests\bar.spec.js for example. Both of them import @playwright/test, but then one of them loads C:\node_modules\playwright and the other loads c:\node_modules\playwright. There's an existing comment in the code that describes this as This forks globals into 2 worlds.

Working around this is easy: Always specify file paths in the same case. #482 did this by making the paths relative.

There's another weird behaviour that plays into this, though. If the c:\foo.js file requires from node_modules, then the Node.js resolution algorithm will sometimes call realpath. This uses some Windows-specific implementation, and it just so happens that realpath normalises c:\node_modules\lib into C:\node_modules\lib. It uppercases the drive letter, leading to the same buggy behaviour we've seen before.

What does this mean? Never ever use paths with lowercase drive letters, and don't be in a CWD that has a lowercase drive letter.

Powershell realised this and made it impossible to go into a lowercase CWD, we did in #482 when we swapped absolute paths with lowercase drive letters for relative ones, and VS Code realised it when they normalize the program argument.

For some reason, this._model.config.workspaceFolder, which we get from VS Code, has a lower-case drive letter though. When we spawn a child process on that CWD in _startBackend, this leads to the bug described above. And this PR fixes it by uppercasing the drive letter.

I've done one final check on my Windows machine, and this still fixes the issue. I'll merge and release this PR, and extend the patch to playwrightTestCLI.ts if we haven't heard any bug reports in a couple weeks.