Test: Update vitest packages

[valentinpalkovic]

Closes #

What I did

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

Caution

This section is mandatory for all contributions. If you believe no manual test is necessary, please state so explicitly. Thanks!

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli-storybook/src/sandbox-templates.ts

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

🦋 Canary release

This PR does not have a canary release associated. You can request a canary release of this pull request by mentioning the @storybookjs/core team here.

core team members can create a canary release here or locally with gh workflow run --repo storybookjs/storybook publish.yml --field pr=<PR_NUMBER>

Summary by CodeRabbit

• Chores

  • Upgraded Vitest-related dependencies to version 4.0.18 across the project.

• Refactor

  • Simplified mocking utilities implementation by leveraging external libraries, reducing internal code complexity.

[coderabbitai]

📝 Walkthrough

Walkthrough

Upgrades Vitest-related packages to version 4.0.18 across multiple package.json files, refactors automock implementation to delegate to @vitest/mocker, removes esmWalker module entirely, and updates resolution entries to reflect new package versions.

Changes

Cohort / File(s)	Summary
Package Version Upgrades code/core/package.json, code/package.json, package.json	Updated Vitest-related packages (@vitest/expect, @vitest/spy, @vitest/mocker, @vitest/utils, and vitest core) from 3.2.4/4.0.14 to 4.0.18; also updated patch resolution for @vitest/expect.
Automock Refactoring code/core/src/mocking-utils/automock.ts	Replaced large in-file automockModule implementation with direct import from @vitest/mocker/automock. Introduced STORYBOOK_GLOBAL_THIS_ACCESSOR constant for globalThis access. Updated getAutomockCode to delegate to imported automockModule with new signature using ParseFn type.
ESM Walker Module Removal code/core/src/mocking-utils/esmWalker.ts	Completely removed esmWalker module with all 343 lines of implementation, including exported functions (esmWalker, setIsNodeInPattern, isNodeInPattern, isStaticProperty, isStaticPropertyKey, isFunctionNode, isInDestructuringAssignment, getArbitraryModuleIdentifier), type exports, and estree re-exports.
Resolution Configuration Update scripts/ecosystem-ci/existing-resolutions.js	Updated EXISTING_RESOLUTIONS set by replacing '@vitest/expect@npm:3.2.4' with '@vitest/expect@npm:4.0.18' entry.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related PRs

• storybookjs/storybook#33315: Modifies mocking-utils surface and changes how Storybook consumes @vitest/mocker, directly overlapping with automock refactoring changes.
• storybookjs/storybook#33086: Performs matching Vitest v4 dependency upgrades with similar package version updates to 4.0.18.
• storybookjs/storybook#33277: Modifies scripts/ecosystem-ci/existing-resolutions.js and updates the EXISTING_RESOLUTIONS exported constant.

✨ Finishing touches

• 📝 Generate docstrings

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[nx-cloud]

View your CI Pipeline Execution ↗ for commit 02ee558

Command	Status	Duration	Result
nx run-many -t compile,check,knip,test,pretty-d...	❌ Failed	1m 15s	View ↗

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☁️ Nx Cloud last updated this comment at 2026-03-03 09:26:37 UTC

[sheremet-va]

Is this really needed now?

[yannbf]

Unfortunately yes, because we support running tests in "portable stories" with Jest. Because the test utilities rely on Vitest utilities, then this clash occurs

[storybook-app-bot]

Package Benchmarks

^{Commit: 01d6f5f, ran on 27 February 2026 at 13:21:20 UTC}

The following packages have significant changes to their size or dependencies:

storybook

	Before	After	Difference
Dependency count	49	45	🎉 -4 🎉
Self size	20.19 MB	20.43 MB	🚨 +236 KB 🚨
Dependency size	16.52 MB	16.15 MB	🎉 -378 KB 🎉
Bundle Size Analyzer	Link	Link

@storybook/cli

	Before	After	Difference
Dependency count	183	179	🎉 -4 🎉
Self size	779 KB	779 KB	0 B
Dependency size	67.37 MB	67.23 MB	🎉 -142 KB 🎉
Bundle Size Analyzer	Link	Link

@storybook/codemod

	Before	After	Difference
Dependency count	176	172	🎉 -4 🎉
Self size	32 KB	32 KB	🚨 +36 B 🚨
Dependency size	65.89 MB	65.75 MB	🎉 -142 KB 🎉
Bundle Size Analyzer	Link	Link

create-storybook

	Before	After	Difference
Dependency count	50	46	🎉 -4 🎉
Self size	1.04 MB	1.04 MB	0 B
Dependency size	36.72 MB	36.57 MB	🎉 -142 KB 🎉
Bundle Size Analyzer	node	node

[github-actions]

	Fails
🚫	PR is marked with "BREAKING CHANGE" label.
🚫	The "#### Manual testing" section must be filled in. Please describe how to test the changes you've made, step by step, so that reviewers can confirm your PR works as intended.

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