Open jthrilly opened 6 months ago
Also having this issue. Is there anything that can be done about this? Seems problematic given that NextJS specifically recommends testing with Vitest:
https://nextjs.org/docs/app/building-your-application/testing/vitest
Link to the code that reproduces this issue
https://github.com/jthrilly/vitest-reproduction
To Reproduce
getServerStuff()
function returns the value correctly, without errors.The example reproduction uses React.cache, but the same is true of any React canary or experimental APIs which are "supported" in Next.
This issue also impacts other test runners, such as the node test runner and bun.
Current vs. Expected behavior
Current behaviour is that
React.cache
is not resolved in the test. Expected behaviour is that any test environment should have access to the same module resolution as the build and dev environments. If this is not the case by default, a compatibility layer must be provided.Provide environment information
Which area(s) are affected? (Select all that apply)
Testing
Which stage(s) are affected? (Select all that apply)
next dev (local), next build (local), next start (local)
Additional context
Unit tests (run via vitest, bun test, or the node test runner) that touch canary or experimental React features fail because they resolve React to the version in package.json, rather than the internal version used by Next.
Additionally, some next subpackage exports cannot be resolved by vittest, such as
next/headers
,next/cache
, etc.These issues have two causes:
next/cache
etc are exported is not compatible with the way that vite ESM module resolution works (a file extension is expected, for some reason).Since vitest is one of the recommended ways to introduce unit testing into a NextJs app (as per the docs), I expect code that works in dev and production to also work in this test environment.
The React issue specifically can be worked around using a resolve alias in vitest that points to
next/dist/compiled/react/cjs/react.development.js
(this is demonstrated in the repro), but this creates a maintenance issue. Regardless of alias config, vitest cannot correctly resolve other next packages such asnext/cache
,next/headers
etc.Bottom line is that there should never be an intentional difference between the dev/prod and test environments. It totally undermines the testing!