NextJS 10 breaks tests by throwing warnings for components using next/link

[thanos-diacakis-grandrounds]

Bug report

Describe the bug

Minimal code to replicate: https://github.com/thanos-diacakis-grandrounds/nextjs-10-link-test-errors

We have a simple component includes a next/link. We have tests that will render the component, and assert various things (assertions omitted in the sample code). This works fine in NextJS 9.5.6. When upgrading to NextJS 10, these tests start throwing the following two warnings:

1. Warning: An update to Link inside a test was not wrapped in act(...). [etc.]
2. Warning: Can't perform a React state update on an unmounted component. This is a no-op, but it indicates a memory leak in your application. To fix, cancel all subscriptions and asynchronous tasks in a useEffect cleanup function.

To Reproduce

1. Check out this repo: https://github.com/thanos-diacakis-grandrounds/nextjs-10-link-test-errors
2. Run "npm run test"
3. Observer the warnings

Expected behavior

We expected to see the same behavior as NextJS 9.x - no warnings.

Screenshots

System information

• OS: macOS 10.15.7
• Version of Next.js: 10.0.3
• Version of Node.js: 14.6.0
• Deployment: local dev with "npm run test"

Additional context

If there is a single test, it seems to pass with no warnings. Once you add more tests, it seems to fail, even if the additional tests do nothing at all.

Removing the resolves the issue.

Tried turning off prefetching, making the act() function async/await, assuming some kind of state change is happening behind the scenes with no luck.

[kfazinic]

I'm getting the same.

[ajw725]

i just spent hours trying to figure out what the heck i was doing wrong. having the same problem.

[mAAdhaTTah]

PR to resolve: #20169. I need to test it fully myself but would appreciate if anyone experiencing this issue could give it a try.

[thanos-diacakis-grandrounds]

@mAAdhaTTah When I install NextJS from your PR, it fails to install "next/babel", and then nothing works. Any idea why?

I am trying to test against your PR to help move it forward.

[mAAdhaTTah]

@thanos-diacakis-grandrounds I tested it by cloning the repo, running the build, and then copying the dist folder into my project's node_modules manually. You can't install a monorepo by pointing the version to a git ref, unfortunately (if that's what you were doing).

[thanos-diacakis-grandrounds]

Thanks for the steps. I have performed those, and I can confirm that it un-breaks all of our tests.

In case anyone else wants to follow this and needs more details:

• Check out James' PR branch of NetxJS
• Assuming you have yarn, run "yarn dev". When it's done building, you can ^c it. It defaults to "watcher" mode.
• Replace your_projects/node_modules/next/dist with james_branch_nextjs/packages/next/dist