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The React Framework
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Testing frameworks (Vitest) cannot correctly resolve React to the internal Next version, causing tests to fail #64782

Closed jthrilly closed 1 week ago

jthrilly commented 1 week ago

Link to the code that reproduces this issue

github.com/jthrilly/vitest-reproduction

To Reproduce

  1. Run or build the application. Note that the getServerStuff function returns the value correctly, without errors.
  2. Run the test task, which triggers vitest. Notice that the test fails because React.cache is being resolved in the package.json version of React, 18.2.

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

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

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 23.4.0: Fri Mar 15 00:12:49 PDT 2024; root:xnu-10063.101.17~1/RELEASE_ARM64_T6020
  Available memory (MB): 32768
  Available CPU cores: 12
Binaries:
  Node: 20.11.0
  npm: 10.2.4
  Yarn: N/A
  pnpm: 8.15.5
Relevant Packages:
  next: 14.2.2 // Latest available version is detected (14.2.2).
  eslint-config-next: 14.2.2
  react: 18.2.0
  react-dom: 18.2.0
  typescript: 5.4.5
Next.js Config:
  output: N/A

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:

  1. Next is using an internal version of React, which is not resolved outside of next specific build/serve commands.
  2. The way 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 as next/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!

github-actions[bot] commented 1 week ago

We could not detect a valid reproduction link. Make sure to follow the bug report template carefully.

Why was this issue closed?

To be able to investigate, we need access to a reproduction to identify what triggered the issue. We need a link to a public GitHub repository (template for App Router, template for Pages Router), but you can also use these templates: CodeSandbox: App Router or CodeSandbox: Pages Router.

The bug template that you filled out has a section called "Link to the code that reproduces this issue", which is where you should provide the link to the reproduction.

What should I do?

Depending on the reason the issue was closed, you can do the following:

In general, assume that we should not go through a lengthy onboarding process at your company code only to be able to verify an issue.

My repository is private and cannot make it public

In most cases, a private repo will not be a sufficient minimal reproduction, as this codebase might contain a lot of unrelated parts that would make our investigation take longer. Please do not make it public. Instead, create a new repository using the templates above, adding the relevant code to reproduce the issue. Common things to look out for:

I did not open this issue, but it is relevant to me, what can I do to help?

Anyone experiencing the same issue is welcome to provide a minimal reproduction following the above steps by opening a new issue.

I think my reproduction is good enough, why aren't you looking into it quickly?

We look into every Next.js issue and constantly monitor open issues for new comments.

However, sometimes we might miss one or two due to the popularity/high traffic of the repository. We apologize, and kindly ask you to refrain from tagging core maintainers, as that will usually not result in increased priority.

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