test: e2e simple next/after test

tests/e2e/simple-app.test.ts

@@ -272,3 +272,36 @@ test('can require CJS module that is not bundled', async ({ simple }) => {
   expect(parsedBody.notBundledCJSModule.isBundled).toEqual(false)
   expect(parsedBody.bundledCJSModule.isBundled).toEqual(true)
 })
+
+test('next/after callback is executed and finishes', async ({ page, simple }) => {
+  test.skip(!nextVersionSatisfies('>=15.0.0'), 'This test is only for Next.js 15+')
+
+  await page.goto(`${simple.url}/after/check`)
+  const pageInfoLocator1 = await page.locator('#page-info')
+  const pageInfo1 = JSON.parse((await pageInfoLocator1.textContent()) ?? '{}')
+
+  expect(typeof pageInfo1?.timestamp, 'Check page should have timestamp').toBe('number')
+
+  await new Promise((resolve) => setTimeout(resolve, 2000))
+
+  await page.goto(`${simple.url}/after/check`)
+  const pageInfoLocator2 = await page.locator('#page-info')
+  const pageInfo2 = JSON.parse((await pageInfoLocator2.textContent()) ?? '{}')
+
+  expect(typeof pageInfo2?.timestamp, 'Check page should have timestamp').toBe('number')
+
+  expect(pageInfo2.timestamp, 'Check page should be cached').toBe(pageInfo1.timestamp)
+
+
+  await page.goto(`${simple.url}/after/trigger`)
+
+  // wait for next/after to trigger revalidation of check page
+  await new Promise((resolve) => setTimeout(resolve, 5000))
+
+  await page.goto(`${simple.url}/after/check`)
+  const pageInfoLocator3 = await page.locator('#page-info')
+  const pageInfo3 = JSON.parse((await pageInfoLocator3.textContent()) ?? '{}')
+
+  expect(typeof pageInfo3?.timestamp, 'Check page should have timestamp').toBe('number')
+  expect(pageInfo3.timestamp, 'Check page should be invalidated with newer timestamp').toBeGreaterThan(pageInfo1.timestamp)
+})

tests/fixtures/simple/app/after/check/page.js

@@ -0,0 +1,13 @@
+export const revalidate = 3600 // arbitrarily long, just so that it doesn't happen during a test run
+
+
+export default async function Page() {
+  const data = {
+    timestamp: Date.now(),
+  }
+  console.log('/timestamp/key/[key] rendered', data)
+
+  return (
+    <div id="page-info">{JSON.stringify(data)}</div>
+  )
+}

tests/fixtures/simple/app/after/trigger/page.js

@@ -0,0 +1,17 @@
+import { revalidatePath } from 'next/cache'
+import { unstable_after as after, connection } from 'next/server'
+
+export default async function Page() {
+  await connection()
+  after(async () => {
+    // this will run after response was sent
+    console.log('after() triggered')
+    console.log('after() sleep 1s')
+    await new Promise((resolve) => setTimeout(resolve, 1000))
+
+    console.log('after() revalidatePath /after/check')
+    revalidatePath('/after/check')
+  })
+
+  return <div>Page with after()</div>
+}

tests/fixtures/simple/next.config.js

@@ -8,6 +8,7 @@ const nextConfig = {
     outputFileTracingIncludes: {
       '/': ['public/**'],
     },
+    after: true
   },
   images: {
     remotePatterns: [