Mocking next files with jest.mock broken in packages

[spence-novata]

What version of Next.js are you using?

12.0.7

What version of Node.js are you using?

14.17.6

What browser are you using?

N/A

What operating system are you using?

macOS

How are you deploying your application?

jest

Describe the Bug

I'm trying to upgrade to Next 12 and cannot get my tests to pass as something strange is going on with jest.mock

If I use jest.mock to mock next/router and require it from my test or indeed my project the mock works as expected. However, if I require the router into another module the original router is required, not the mock.

I also tried to mock next/dist/client/script and found similar behavior so I don't think this is limited to the router. Adding my own file to the next/dist/client directory and it can be mocked fine. Changing the contents of one of the existing files to match my own test file in there did not though. I was unable to find anything in the package that made these files special and so that is a far as I was able to investigate.

Expected Behavior

The router should be mocked everywhere.

To Reproduce

node_modules/my-module/index.js

const router = require('next/router')

module.exports = {
  name: 'my-module',
  router,
}

app.js

const router = require('next/router')

module.exports = {
  name: 'app stuf',
  router,
}

tests/routerMock.test.js

const router = require('next/router')
const app = require('../app')
const myModule = require('my-module')

jest.mock('next/router', () => ({ isMocked: 'IS MOCKED' }))

describe('Router', () => {
  // PASSES
  it('is mocked in test', () => { 
    expect(router).toEqual({ isMocked: 'IS MOCKED' }) 
  })
  // PASSES
  it('is mocked in app', () => {
    expect(app.router).toEqual({ isMocked: 'IS MOCKED' })
  })
  // FAILS
  it('is mocked in other modules', () => {
    expect(myModule.router).toEqual({ isMocked: 'IS MOCKED' })
  })
})

[timneutkens]

Are you using next/jest or another configuration?

[spence-novata]

This appears to have been fixed in #33731 and 12.0.10

[github-actions]

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