Combining preact and with-jest examples results in production build error

[timmywil]

Example: I've updated the with-jest example to also include preact to reproduce this issue.

Essentially, react-test-renderer relies on a private file in react that isn't present in preact. When bundling for production, that file obviously isn't present. However, there's no point in bundling anything in a __tests__ folder as none of that will get served in production.

This used to work fine in 2.0.0-beta.41, but I think the 2 webpack commits in 2.0.0-beta.42 exposed the fact that the __tests__ directories are being included in the loaders when bundling for production. I was using config.externals in my next.config.js, but I think the new chunk plugin addition isn't respecting that option somehow. If this can be resolved through webpack config, I would welcome any suggestions.

I think one solution would be to exclude directories matching /\/(?:__)?test/ or something in the default webpack config in next.js.

[timmywil]

I figured out that setting config.externals to ['react-test-renderer'] prevents the error, but JS files in the pages/__tests__ directory are still bundled as if they were pages.

[timmywil]

OK, I don't think there's a good solution to this on your end. I worked around it by moving pages/__tests__ to the top-level directory and ensuring that all files within pages were actually bundle-able. The config.externals option also becomes unnecessary at that point.

I'll close this, but I recommend documenting somewhere that even tests should not be placed in the pages directory.

[sedubois]

Maybe better to keep issue open in that case :)