Improve experimental test proxy

[agadzik]

Followup on #52520 and #54014

Enhancements

• Removes --experimental-test-proxy CLI argument from next dev and next start
• Adds a new experimental config option testProxy?: boolean
• Instead of throwing an error, return the originalFetch response if the current request context does not contain the Next-Test-* HTTP headers

Why?
These changes allow us to write mixed Integration + E2E tests within the same Playwright process.

// some-page.spec.ts

test.describe('/some-page', () => {
	test('some integration test', async ({ page, next }) => {
	  // by using the `next` fixture, playwright will send the `Next-Test-*` HTTP headers for 
	  // every request in this test's context.
	  next.onFetch(...);
	  
	  await page.goto(...);
	  await expect(...).toBe('some-mocked-value');
	});

	test('some e2e test', async ({ page }) => {
	  // by NOT using the `next` fixture, playwright does not send the `Next-Test-*` HTTP headers
	  await page.goto(...);
	  await expect(...).toBe('some-real-value');
	});
})

Now I can run next dev and locally develop my App Router pages AND run my Playwright tests against instead of having to,

• run next dev to locally develop my change
• ctrl+c to kill server
• run next dev --experimental-test-proxy to locally run my integration tests

[ijjk]

Allow CI Workflow Run

• approve CI run for commit: 5a7d70d

Note: this should only be enabled once the PR is ready to go and can only be enabled by a maintainer

[ijjk]

Allow CI Workflow Run

• approve CI run for commit: 58a50e2

Note: this should only be enabled once the PR is ready to go and can only be enabled by a maintainer

[mxschmitt]

Hey @agadzik! happy to see such an integration, we at Playwright are currently in the process of doing something on the Playwright level and comparing different approaches, like e.g. ssr (which is similar to the Next.js experimental feature except it has a webServer per worker and WS as a transport in between instead of http-proxy).

I saw also @dvoytenko's initial work in #52520 which introduced it which looks awesome.

Would be curious about your experience with this integration, especially having a global webserver vs. webServer per worker. Do you plan to move it out of experimental soon? We might add something similar to Playwright, so I would be more than happy to talk!

[ijjk]

Stats from current PR

Default Build (Increase detected ⚠️)

General

	vercel/next.js canary	agadzik/next.js gadzik/improve-experimental-test-proxy	Change
buildDuration	13.8s	14s	⚠️ +183ms
buildDurationCached	7.4s	6.6s	N/A
nodeModulesSize	198 MB	198 MB	N/A
nextStartRea..uration (ms)	436ms	442ms	N/A

Client Bundles (main, webpack)

	vercel/next.js canary	agadzik/next.js gadzik/improve-experimental-test-proxy	Change
2453-HASH.js gzip	30.8 kB	30.8 kB	N/A
3304.HASH.js gzip	181 B	181 B	✓
3f784ff6-HASH.js gzip	53.7 kB	53.7 kB	✓
8299-HASH.js gzip	5.04 kB	5.04 kB	N/A
framework-HASH.js gzip	45.2 kB	45.2 kB	✓
main-app-HASH.js gzip	242 B	242 B	✓
main-HASH.js gzip	32.2 kB	32.2 kB	N/A
webpack-HASH.js gzip	1.68 kB	1.68 kB	N/A
Overall change	99.3 kB	99.3 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	agadzik/next.js gadzik/improve-experimental-test-proxy	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	agadzik/next.js gadzik/improve-experimental-test-proxy	Change
_app-HASH.js gzip	196 B	197 B	N/A
_error-HASH.js gzip	184 B	184 B	✓
amp-HASH.js gzip	505 B	505 B	✓
css-HASH.js gzip	324 B	325 B	N/A
dynamic-HASH.js gzip	2.5 kB	2.5 kB	N/A
edge-ssr-HASH.js gzip	258 B	258 B	✓
head-HASH.js gzip	352 B	352 B	✓
hooks-HASH.js gzip	370 B	371 B	N/A
image-HASH.js gzip	4.21 kB	4.21 kB	✓
index-HASH.js gzip	259 B	259 B	✓
link-HASH.js gzip	2.67 kB	2.67 kB	N/A
routerDirect..HASH.js gzip	314 B	312 B	N/A
script-HASH.js gzip	386 B	386 B	✓
withRouter-HASH.js gzip	309 B	309 B	✓
1afbb74e6ecf..834.css gzip	106 B	106 B	✓
Overall change	6.57 kB	6.57 kB	✓

Client Build Manifests

	vercel/next.js canary	agadzik/next.js gadzik/improve-experimental-test-proxy	Change
_buildManifest.js gzip	481 B	484 B	N/A
Overall change	0 B	0 B	✓

Rendered Page Sizes

	vercel/next.js canary	agadzik/next.js gadzik/improve-experimental-test-proxy	Change
index.html gzip	529 B	529 B	✓
link.html gzip	542 B	541 B	N/A
withRouter.html gzip	525 B	523 B	N/A
Overall change	529 B	529 B	✓

Edge SSR bundle Size

	vercel/next.js canary	agadzik/next.js gadzik/improve-experimental-test-proxy	Change
edge-ssr.js gzip	95.3 kB	95.3 kB	N/A
page.js gzip	3.04 kB	3.04 kB	N/A
Overall change	0 B	0 B	✓

Middleware size

	vercel/next.js canary	agadzik/next.js gadzik/improve-experimental-test-proxy	Change
middleware-b..fest.js gzip	625 B	624 B	N/A
middleware-r..fest.js gzip	151 B	151 B	✓
middleware.js gzip	25.5 kB	25.5 kB	N/A
edge-runtime..pack.js gzip	839 B	839 B	✓
Overall change	990 B	990 B	✓

Next Runtimes

	vercel/next.js canary	agadzik/next.js gadzik/improve-experimental-test-proxy	Change
app-page-exp...dev.js gzip	170 kB	170 kB	✓
app-page-exp..prod.js gzip	96.9 kB	96.9 kB	✓
app-page-tur..prod.js gzip	98.6 kB	98.6 kB	✓
app-page-tur..prod.js gzip	93.1 kB	93.1 kB	✓
app-page.run...dev.js gzip	144 kB	144 kB	✓
app-page.run..prod.js gzip	91.5 kB	91.5 kB	✓
app-route-ex...dev.js gzip	21.4 kB	21.4 kB	✓
app-route-ex..prod.js gzip	15.1 kB	15.1 kB	✓
app-route-tu..prod.js gzip	15.1 kB	15.1 kB	✓
app-route-tu..prod.js gzip	14.8 kB	14.8 kB	✓
app-route.ru...dev.js gzip	21 kB	21 kB	✓
app-route.ru..prod.js gzip	14.8 kB	14.8 kB	✓
pages-api-tu..prod.js gzip	9.54 kB	9.54 kB	✓
pages-api.ru...dev.js gzip	9.81 kB	9.81 kB	✓
pages-api.ru..prod.js gzip	9.54 kB	9.54 kB	✓
pages-turbo...prod.js gzip	22.4 kB	22.4 kB	✓
pages.runtim...dev.js gzip	23.1 kB	23.1 kB	✓
pages.runtim..prod.js gzip	22.4 kB	22.4 kB	✓
server.runti..prod.js gzip	50.9 kB	50.9 kB	✓
Overall change	945 kB	945 kB	✓

build cache Overall increase ⚠️

	vercel/next.js canary	agadzik/next.js gadzik/improve-experimental-test-proxy	Change
0.pack gzip	1.57 MB	1.57 MB	⚠️ +651 B
index.pack gzip	105 kB	106 kB	⚠️ +479 B
Overall change	1.67 MB	1.67 MB	⚠️ +1.13 kB

Diff details

Diff for middleware.js

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Diff for edge-ssr.js

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Commit: 58a50e2

[ijjk]

Tests Passed