CSF: Add Storybook test syntax (Storybook v9)

[yannbf]

Closes #32244

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

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 pull request has been released as version 0.0.0-pr-32391-sha-41c83af5. Try it out in a new sandbox by running npx storybook@0.0.0-pr-32391-sha-41c83af5 sandbox or in an existing project with npx storybook@0.0.0-pr-32391-sha-41c83af5 upgrade.

More information

Published version	0.0.0-pr-32391-sha-41c83af5
Triggered by	@yannbf
Repository	storybookjs/storybook
Branch	feature/test-syntax-in-csf
Commit	41c83af5
Datetime	Thu Sep 4 18:48:24 UTC 2025 (1757011704)
Workflow run	17473700454

To request a new release of this pull request, mention the @storybookjs/core team.

core team members can create a new canary release here or locally with gh workflow run --repo storybookjs/storybook canary-release-pr.yml --field pr=32391

Greptile Summary

Updated On: 2025-09-03 17:13:50 UTC

This PR introduces a comprehensive test syntax feature for Storybook's Component Story Format (CSF) that allows developers to define test functions directly on stories using a .test() method. The changes implement a new hierarchical story/test relationship where tests become child entries of their parent stories.

Key Changes:

Core Architecture:

• Extends StoryIndexEntry with a subtype field ('story' | 'test') to distinguish between regular stories and test entries
• Adds parent and parentName fields for test entries to establish hierarchical relationships
• Introduces API_TestEntry type alongside existing API_StoryEntry for type safety

Test Syntax API:

• Stories now support .test(name, testFn) and .test(name, overrides, testFn) method calls
• Test functions receive the same StoryContext as play functions and can be async or sync
• Tests inherit parent story's args, parameters, and globals but can override them
• Tests are automatically tagged with 'test-fn' and '!autodocs' to distinguish them from regular stories

UI Integration:

• Adds TestNode components to the sidebar with dedicated test icons (beaker icon in green)
• Stories with tests become expandable branch nodes in the sidebar tree
• Enhanced tag filtering system with support for tag presets, inverted filtering, and test-specific tags
• Search results and story navigation updated to handle test subtypes

Indexing and Processing:

• CSF parser extended to detect .test() method calls and extract test metadata
• Story indexer generates separate index entries for tests using toTestId() function with colon separator (e.g., storyId:testName)
• Vitest integration updated to support running individual tests within stories

Type System Updates:

• All existing story entries systematically updated to include subtype: 'story'
• New TestFunction type introduced parallel to existing PlayFunction
• Enhanced type safety across manager API and preview components

The feature enables a new testing paradigm where component tests can be co-located with their stories, inheriting story configuration while providing test-specific overrides. This creates a more integrated testing experience within the Storybook ecosystem.

PR Description Notes:

• The PR description is incomplete - the "What I did" section is empty and no issue number is provided
• None of the testing checkboxes are marked, despite this being a major feature addition
• The manual testing section contains only placeholder text