docs: document promise unwrapping

[Andreas (AndyOGo)]

fixes #39027

Inspired by similar Jest's modifiers .resolves/.rejects.

• Double check proper version
• Double check return type
• Maybe a guide like Jest "Testing Asynchronous Code - .resolves/.rejects" guide would be desireable as well

[Andreas (AndyOGo)]

@microsoft-github-policy-service agree

[Yury Semikhatsky (yury-s)]

The change looks good, but lint is not happy. You need to update type overrides in utils/generate_types/overrides-test.d.ts.

[Yury Semikhatsky (yury-s)]

The change looks good, but lint is not happy.

[Andreas (AndyOGo)]

The change looks good, but lint is not happy.

Yury Semikhatsky (@yury-s) Okay. That lint step here passed. Is there another lint I should check?
https://github.com/microsoft/playwright/actions/runs/23310423478/job/67858093654?pr=39719

[github-actions]

Test results for "MCP"

5507 passed, 343 skipped

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Merge workflow run.

[github-actions]

Test results for "tests 1"

10 flaky

⚠️ [chromium-library] › library/trace-viewer.spec.ts:1223 › should display language-specific locators `@ubuntu-22.04-chromium-tip-of-tree`
⚠️ [chromium-library] › library/popup.spec.ts:261 › should not throw when click closes popup `@chromium-ubuntu-22.04-arm-node20`
⚠️ [chromium-library] › library/video.spec.ts:358 › screencast › should capture navigation `@chromium-ubuntu-22.04-arm-node20`
⚠️ [chromium-library] › library/popup.spec.ts:261 › should not throw when click closes popup `@chromium-ubuntu-22.04-node24`
⚠️ [chromium-library] › library/trace-viewer.spec.ts:1223 › should display language-specific locators `@chromium-ubuntu-22.04-node20`
⚠️ [chromium-library] › library/popup.spec.ts:261 › should not throw when click closes popup `@chromium-ubuntu-22.04-node22`
⚠️ [webkit-library] › library/screencast.spec.ts:85 › start reuses existing screencast when video recording is running `@webkit-ubuntu-22.04-node20`
⚠️ [webkit-library] › library/trace-viewer.spec.ts:1223 › should display language-specific locators `@webkit-ubuntu-22.04-node20`
⚠️ [webkit-page] › page/page-network-request.spec.ts:288 › should parse the data if content-type is application/x-www-form-urlencoded `@webkit-ubuntu-22.04-node20`
⚠️ [playwright-test] › ui-mode-trace.spec.ts:465 › should filter actions tab on double-click `@windows-latest-node20`

38811 passed, 845 skipped

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Merge workflow run.