Testing middleware with Jest: TypeError: this._headers.getAll is not a function

Verify canary release

• I verified that the issue exists in the latest Next.js canary release

Provide environment information

Operating System: Platform: darwin Arch: arm64 Version: Darwin Kernel Version 21.6.0: Mon Aug 22 20:20:05 PDT 2022; root:xnu-8020.140.49~2/RELEASE_ARM64_T8101

Binaries: Node: 18.9.0 npm: 8.19.1 Yarn: 1.22.19 pnpm: N/A

Relevant packages: next: 13.0.2-canary.0 eslint-config-next: N/A react: 18.2.0 react-dom: 18.2.0

What browser are you using? (if relevant)

No response

How are you deploying your application? (if relevant)

No response

Describe the Bug

Hello everybody,

I am currently having issues trying to test the middleware.ts in my project, and to reproduce it, I’ve created a small project from next.js/examples/with-jest template, and here is the repo.

The middleware:

export function middleware(req: NextRequest) {
    console.log('Hello')
    return NextResponse.next({headers: new Headers()})
}

The test:

describe('Middleware', () => {
  it('middleware', async () => {
    const res = await middleware(new NextRequest('http://localhost/'))

    console.log('res', res)
  })
})

Other findings:

I’ve also dug a little bit, and it seems that node_modules/next/server/web/spec-extension/cookies/response-cookies.ts:36:35 is expected to fail, I just don’t know in which circumstances:

Other things I’ve tried:

Changing jestEnvironment to node didn’t yield the expected result. I’ve done it by adding the following comment in the test:

/**
 * @jest-environment node
 */

Thanks in advance

Expected Behavior

I expect to be able to test the middleware.

Link to reproduction

https://github.com/firatgh/nextjs-with-jest

To Reproduce

yarn test

[BolajiAyodeji]

Same issue for me with Next13 on Netlify.

[AndrewVos]

This happens for me in production when I upgrade to Next.js 13:

Literally just some text. This is on Netlify.