SyntaxError: Unexpected token 'export' when using Jest

[ClementDreptin]

Description

Since the recent move of next-intl to ESM, running tests with Jest broke.

Verifications

• I've verified that the problem I'm experiencing isn't covered in the docs.
• I've searched for similar, existing issues on GitHub and Stack Overflow.
• I've compared my app to a working example to look for differences.

Mandatory reproduction URL

https://github.com/amannn/next-intl/tree/main/examples/example-app-router

Reproduction description

1. Clone the example-app-router example app.
2. Run the test:jest script that is in package.json.

Expected behaviour

I expect Jest to run the tests successfully.

What I tried

I feel like I tested just about every configuration combination possible in tsconfig.json and jest.config.ts and followed the Jest docs about using ES modules, to no avail.

I noticed that in #1470 the first breaking change mentioned is

The CommonJS build has been removed. While most tools support ESM out-of-the-box, some might require additional configuration (e.g. Jest might benefit from next/jest).

but I'm not sure what you mean by "Jest might benefit from next/jest", this is probably where I missed something.

[service-paradis]

I also face similar problems using vitest since the upgrade to next-intl@v4.

Ex.

Error: Cannot find module '{project_path}/node_modules/next/server' imported from {project_path}/node_modules/next-intl/dist/esm/development/middleware/middleware.js
Did you mean to import "next/server.js"?

Not sure if this is expected, but I needed to add the following in vitest.config.mts defineConfig:

    deps: {
      inline: ['next-intl'],
    },

[amannn]

@ClementDreptin Thank you for raising this issue! Somehow the Jest examples in this repo still worked, but I can confirm that usage outside of this repo needed an adjustment. I've now updated the examples in this repo.

@service-paradis Also many thanks for your comment! next-intl@4 had to add a workaround to avoid a deoptimization in Next.js, it seems like this (rightfully!) trips up Vitest.

I've now added new testing docs that address both issues raised in this thread and have also linked to this page from the release notes.

Thanks again for sharing your findings and sorry for the trouble! I hope that in a future where vercel/next.js#77200 is fixed and tools like Jest support ESM natively, we can get rid of these workarounds that are necessary for the time being!

[service-paradis]

Thank you for your work on this package and for the follow-up!

[ClementDreptin]

Thank you very much for the very quick fix!