Migrate active unit tests from Jest to Vitest

[ciampo]

What?

See #80855.

TL;DR: Migrates the active package and integration test suites from Jest APIs to explicit Vitest imports, mocks, timers, snapshots, and project-scoped environments. The stack now routes 1,001 tests through Vitest and leaves five Jest tooling suites for the dedicated cleanup/cutover PRs.

Why?

This is the main test-conversion step in the consolidated Jest-to-Vitest migration. It preserves the existing test intent and CI partition while making Vitest the runner for nearly the entire active suite.

How?

• Converts package and integration tests to explicit vitest APIs with globals disabled.
• Routes browser-like tests to jsdom and platform/tooling tests to Node without per-file environment directives.
• Preserves Babel behavior, package source aliases, CSS/worker/WASM mocks, setup order, console matchers, fake timers, snapshot serializers, source locations, sharding, date/timezone coverage, and Flakiness.io identity.
• Adds exact routed-test type checking and requires each owning workspace to declare the same Vitest version.
• Adds narrow temporary bridges for the untyped @wordpress/block-editor store and @wordpress/interface package; publishing complete package declarations remains the follow-up documented in Migrate JavaScript unit and integration tests from Jest to Vitest #80855.
• Makes the 100,000-block reducer test's 10-second headroom explicit. Jest allowed the synchronous operation to finish after five seconds, while Vitest reports its five-second elapsed timeout after the operation returns.
• Marks mocked taxonomy records and queries resolved so shard ordering cannot leave a late Core Data network request.
• Keeps the five remaining Jest tooling suites explicitly isolated for the later browser/tooling and final-cleanup PRs.

Snapshot review

All 79 changed snapshot files were reviewed. Changes are runner headers and nested-suite key formatting, except for the tested Emotion serializer normalization that replaces generated hashes while retaining stable component labels.

Testing Instructions

npm run test:unit:routing
npm run test:unit:conventions
npm run test:unit -- --runInBand
npm run test:unit:vitest -- --shard=1/4
npm run test:unit:vitest -- --shard=2/4
npm run test:unit:vitest -- --shard=3/4
npm run test:unit:vitest -- --shard=4/4
npm run test:unit:vitest -- --project vitest --run packages/block-editor/src/store/test/performance.js
npm run lint:js -- --quiet
npm run lint:pkg-json
npm run lint:lockfile
npm run lint:tsconfig

The focused PostTaxonomies test, exact 1,001-file Vitest convention/type graph, and rebuilt full stack pass after resolving the taxonomy fixture. The repository-wide Markdown and dependency lint commands still report their pre-existing baselines; the changed documentation lines introduce no new Markdown violations.

Testing Instructions for Keyboard

Not applicable; this changes test infrastructure and test implementations, not UI behavior.

Screenshots or screencast

Not applicable.

Use of AI Tools

Codex was used to implement the migration, run verification, and perform adversarial self-review. The results and changes were reviewed by the author.

[github-actions]

Size Change: +8 B (0%)

Total Size: 7.76 MB

📦 View Changed

Filename	Size	Change
build/scripts/compose/index.min.js	11.6 kB	+2 B (+0.02%)
build/scripts/editor/index.min.js	500 kB	+6 B (0%)

_{compressed-size-action}

[github-actions]

Flaky tests detected in 58ecf75.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/30582519123
📝 Reported issues:

• [Flaky Test] sort patterns #79882 in /test/e2e/specs/site-editor/patterns.spec.js