[Workers] Add Vitest 3 to Vitest 4 migration guide for vitest-pool-workers

[MattieTK]

Summary

Adds a new how-to page, Migrate from Vitest 3 to Vitest 4, under the Workers Vitest integration migration guides. It documents migrating @cloudflare/vitest-pool-workers from v0.12.x (Vitest 3) to v0.13.x (Vitest 4): the cloudflareTest() plugin config API, the jscodeshift codemod, the isolatedStorage/singleWorker removal, the deprecated cloudflare:test imports (env/SELF moving to cloudflare:workers), and the fetchMock removal.

The source material is the v0.13.0 release notes (cloudflare/workers-sdk#11632), as suggested during review of #29465. This supersedes that closed PR and addresses #29463.

Content was validated line by line against the published package (npm @cloudflare/vitest-pool-workers 0.13.0 and the current 0.16.18): the shipped type definitions, the codemod source, and the source PR body. Two points were corrected relative to the source changelog wording:

• env and SELF from cloudflare:test are deprecated, not removed — they are still exported (with @deprecated JSDoc) in both 0.13.0 and 0.16.18, so migration is recommended rather than required. fetchMock, by contrast, is genuinely removed.
• The codemod transforms only defineWorkersProject. Both defineWorkersProject and defineWorkersConfig were removed from the API, but a config using defineWorkersConfig must be migrated by hand.

Documentation checklist

• The change adheres to the documentation style guide.
• If a larger change - such as adding a new page- an issue has been opened in relation to any incorrect or out of date information that this PR fixes.

[github-actions]

This pull request requires reviews from CODEOWNERS as it changes files that match the following patterns:

Pattern	Owners
/src/content/docs/workers/	@cloudflare/workers-docs, @GregBrimble, @irvinebroque, @mikenomitch, @korinne, @WalshyDev, @cloudflare/deploy-config, @cloudflare/product-owners, @cloudflare/wrangler, @MattieTK, @cloudflare/dev-plat-leads, @vy-ton

[ask-bonk]

Posted 2 inline suggestions.

• MEDIUM src/content/docs/workers/testing/vitest-integration/migration-guides/migrate-from-vitest-3-to-vitest-4.mdx:62 — Directional language ("below") violates the style guide.
• LOW src/content/docs/workers/testing/vitest-integration/migration-guides/migrate-from-vitest-3-to-vitest-4.mdx:22 — Sentence can be tightened for clarity.

Consider using a permalink with a full commit hash for the GitHub example link on line 119, since main branch links can break if the fixture is reorganized.

[ask-bonk]

Review complete.

Labels applied: documentation, product:workers, content:new

Validation run: pnpm run check passed with 0 errors related to this change.

Posted review: PR #31648 review

The PR is technically accurate and well-structured. I found two minor style items to address:

• MEDIUM — Line 62 uses directional language ("below"), which the style guide prohibits.
• LOW — Line 22 can be tightened for clarity.

I also noted that the GitHub example link on line 119 points to main rather than a permalink with a commit hash, so it may break if the fixture is reorganized in the future.

github run

[github-actions]

Preview URL: https://d14dbdbb.preview.developers.cloudflare.com
Preview Branch URL: https://vitest-pool-workers-migrate-to-vitest-4.preview.developers.cloudflare.com

Files with changes (up to 15)

Original Link	Updated Link
https://developers.cloudflare.com/workers/testing/vitest-integration/migration-guides/migrate-from-vitest-3-to-vitest-4/	https://vitest-pool-workers-migrate-to-vitest-4.preview.developers.cloudflare.com/workers/testing/vitest-integration/migration-guides/migrate-from-vitest-3-to-vitest-4/

[cloudflare-docs-bot]

Review

⚠️ Part of the review could not complete in commit d14dbdb — it will retry on the next push.

Code Review

This code review is in beta and may not always be helpful — use your judgment.

✅ No code review issues found.

Style Guide Review

❌ This review could not complete this run; results may be incomplete. It will retry on the next push.

Commands

Only codeowners can run commands. Post a comment with the command to trigger it.

Command	Description
/review	Runs a review now. Incremental if a prior review exists, full if not.
/full-review	Re-reviews the entire PR diff from scratch, ignoring incremental history. Useful after a rebase, when you want a fresh review, or if the bot gets out of sync and reports issues that no longer exist.
/ignore-review-limit	Permanently lifts the 2-review automatic limit for this PR. Future pushes will trigger reviews as normal.

[irvinebroque]

Love it