vitest-pool-workers does not run Wrangler custom builds

[GregBrimble]

What versions & operating system are you using?

wrangler 4.22.0, vitest 3.1.4 and @cloudflare/vitest-pool-workers 0.8.48

Please provide a link to a minimal reproduction

No response

Describe the Bug

When configuring vitest-pool-workers, pointing at a Wrangler config file which relies on a custom build does not work. I'd expect the custom build to run, but it does not.

Please provide any relevant error logs

No response

[jamesopstad]

I think this is unlikely to be supported as Vitest builds dynamically watches test files to determine which files to rebuild. It would be good to know more about your use case so we can see if there's another way we could support it.

[GregBrimble]

I was trying to work around #7324 when I noticed custom builds also don't work (so I couldn't pre-bundle stuff). If #7324 gets fixed, I'm happy!

[dario-piotrowicz]

I've updated this issue to be just for documentation, since (as stated in Jame's reply above) this seems to be expected, so I think that we should just document somewhere, probably https://developers.cloudflare.com/workers/testing/vitest-integration/configuration/#workerspooloptions, that the build filed is not applicable for vitest.

I think that this is somewhat already covered by this sentence:

But I think that we might as well just call out more specifically that various fields of wrangler config files are not supported/considered.

[petebacondarwin]

The motivation for this feature request was driven by the need to pre-compile a Worker to get the unenv polyfills included.
We are getting close to not needing the polyfills at all in workerd then this issue is going to go away quite soon.
Leaving this in the backlog with low priority to come back to and check when we believe it is no longer an issue.