feat(test runner): server side mocking

[Skn0tt]

Implements #30766.

Adds an HTTP proxy that application servers can route their network traffic through to make it subject to Playwright routes.

[vitalets]

Hi @Skn0tt @dgozman
I've recently discovered that Next.js has an experimental flag to mock server-side requests with Playwright:
https://github.com/vercel/next.js/blob/canary/packages/next/src/experimental/testmode/playwright/README.md

Just curios, how does it relates to this PR? Seems like they provide own fixtures for running proxy as well..

[Skn0tt]

Just curios, how does it relates to this PR? Seems like they provide own fixtures for running proxy as well..

Their experiment tries to solve the same problem in a very similar manner to this. It doesn't look like a lot happened to that experiment in Next.js, and it's not even in the docs. So I could imagine that they'll recommend our mocking proxy instead.

[Skn0tt]

cc @dvoytenko @ijjk for visibility

[MindaugasMateika]

Hi @Skn0tt @dgozman I've recently discovered that Next.js has an experimental flag to mock server-side requests with Playwright: https://github.com/vercel/next.js/blob/canary/packages/next/src/experimental/testmode/playwright/README.md

Just curios, how does it relates to this PR? Seems like they provide own fixtures for running proxy as well..

Third-party implementations, such as msw, playwright-msw and others, have always been available for those who wanted server-side mocking. However, it doesn't compare with having server-side mocking built directly into Playwright which will offer parallel support, bug fixes, and most imporantly peace of mind knowing it will remain working with future releases ❤️ My 2 cents, not a contributor.

[Skn0tt]

From my understanding of playwright-msw, it's about mocking browser requests. This work is about mocking server requests, which is different.

[github-actions]

Test results for "tests 1"

1 failed
❌ [playwright-test] › tests/reporter-html.spec.ts:2680:5 › merged › execSync doesnt produce a second stdout attachment @macos-latest-node18-2

13 flaky

⚠️ [firefox-page] › tests/page/page-evaluate.spec.ts:403:3 › should throw for too deep reference chain @firefox-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/browsercontext-proxy.spec.ts:27:3 › should work when passing the proxy only on the context level @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/browsertype-connect.spec.ts:554:5 › launchServer › should error when saving download after deletion @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/inspector/cli-codegen-2.spec.ts:24:7 › cli codegen › should contain open page @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/proxy.spec.ts:93:11 › should proxy local network requests › with other bypasses › link-local @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/proxy.spec.ts:228:3 › should use socks proxy @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/proxy.spec.ts:238:3 › should use socks proxy in second page @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/selector-generator.spec.ts:129:5 › selector generator › should use ordinal for identical nodes @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/selector-generator.spec.ts:437:5 › selector generator › should ignore empty aria-label for candidate consideration @webkit-ubuntu-22.04-node18
⚠️ [webkit-library] › tests/library/trace-viewer.spec.ts:109:1 › should show tracing.group in the action list with location @webkit-ubuntu-22.04-node18
⚠️ [webkit-page] › tests/page/page-leaks.spec.ts:82:5 › click should not leak @webkit-ubuntu-22.04-node18
⚠️ [webkit-page] › tests/page/page-leaks.spec.ts:107:5 › fill should not leak @webkit-ubuntu-22.04-node18
⚠️ [webkit-page] › tests/page/page-leaks.spec.ts:161:5 › waitFor should not leak @webkit-ubuntu-22.04-node18

37848 passed, 655 skipped
✔️✔️✔️

Merge workflow run.