Migrate the testing environment to Vitest: rename equalMarkup to toEqualMarkup and remove the automated test runner

[pomek]

🚀 Summary

Migrates the testing environment to Vitest and removes the automated test runner.

equalMarkup → toEqualMarkup(): the Chai assertion is renamed to a Vitest matcher (matching the Vitest naming style) and the unused attribute Chai assertion is removed. The matcher is registered in a Vitest setup file via expect.extend( { toEqualMarkup } ), importing it from the main entry point of @ckeditor/ckeditor5-dev-tests, which is now browser-safe (it exposes only the matcher). The package ships the vitest type augmentation (lib/vitest/matchers.d.ts), so consumers get the typings out of the box.

Automated test runner removal: the ckeditor5-dev-tests-run-automated binary and the whole Karma testing environment are removed — automated tests are executed directly with Vitest using the packages' own test scripts. This covers bin/testautomated.js and the runAutomatedTests() task, the whole lib/utils/automated-tests/ directory (Karma and webpack configuration, reporters, leak detectors), the automated CLI options in parseArguments() (including --production — the strict checks live in each package's Vitest setup and apply in every run, so local and CI executions follow the same rules), desktop notifications (node-notifier), the IntelliJ Karma integration, 26 dependencies of ckeditor5-dev-tests, and loaders.getCoverageLoader() with its babel-loader dependency in ckeditor5-dev-utils.

The package now provides the manual test server (ckeditor5-dev-tests-run-manual, untouched) and the toEqualMarkup() Vitest matcher.

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📌 Related issues

• Closes ckeditor/ckeditor5-internal#4595

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💡 Additional information

• Replaces Rename the equalMarkup Chai assertion to the toEqualMarkup Vitest matcher #1412 — both changes are combined here, as the matcher migration and the runner removal are tightly coupled (the Karma entry-file generator was the only in-repo registrar of the old assertions).
• The attribute Chai assertion had zero call sites in ckeditor5 and ckeditor5-commercial, hence it is removed instead of migrated (a deviation from the issue's DoD).
• Consumer adoption (setup files, ~1800 call-site renames, pnpm-based test runs): ckeditor/ckeditor5-commercial#10862 — after it, neither repository calls the automated binary.
• Because ckeditor5-dev-tests was the only workspace package with a postinstall script, the root scripts/postinstall.js now uses pnpm run -r --if-present postinstall.
• Changelog entries (major breaking changes) are included.

[psmyrek]

Two changelog entries describe more or less the same change:

• .changelog/20260706081519_ci_4595_to_equal_markup_vitest_matcher.md
• .changelog/20260706081521_ci_4595_to_equal_markup_vitest_matcher.md

Would it be possible to merge these messages together?

[cursor]

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