Storybook Testing — Storybook 10

Overview

Storybook 10 unifies component testing into a single workflow: interaction tests via play() functions, visual regression via Chromatic TurboSnap, and accessibility audits via the a11y addon — all running through Vitest. Stories are executable test specifications, not just documentation.

What's new in Storybook 10 (vs 9):

• ESM-only enforced — the single breaking change; Node 20.16+ / 22.19+ / 24+ required; 29% smaller install
• Module automocking (sb.mock) — build-time module mocking, scoped per-project in preview.ts
• CSF factories (React, preview) — defineMain → definePreview → preview.meta() → meta.story() chain
• Essential addons in core — viewport, controls, interactions, actions no longer separate deps
• Import path changes — @storybook/test → storybook/test (old paths still work as aliases)
• React Server Component story support — test RSC in isolation
• Vitest 4 support — experimental-addon-test renamed to addon-vitest

When to use this skill:

• Writing component stories in CSF3 format with TypeScript
• Setting up interaction tests with play() functions
• Configuring Chromatic visual regression with TurboSnap
• Using module automocking at the story level
• Running accessibility tests in CI via the a11y addon
• Generating living documentation with autodocs
• Migrating from Storybook 9 to 10

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Quick Reference

Rule	Impact	Description
storybook-csf3-factories	HIGH	Typesafe CSF3 story factories with satisfies Meta
storybook-play-functions	CRITICAL	Interaction testing with play() and @storybook/test
storybook-vitest-integration	HIGH	Run stories as Vitest tests via @storybook/addon-vitest
storybook-chromatic-turbosnap	HIGH	TurboSnap reduces snapshot cost 60-90%
storybook-sb-mock	HIGH	Story-level module mocking with sb.mock
storybook-a11y-testing	CRITICAL	Automated axe-core accessibility scans in CI
storybook-autodocs	MEDIUM	Auto-generated docs from stories

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Storybook Testing Pyramid

         ┌──────────────┐
         │   Visual     │  Chromatic TurboSnap
         │  Regression  │  (snapshot diffs)
         ├──────────────┤
         │ Accessibility│  @storybook/addon-a11y
         │   (a11y)     │  (axe-core scans)
         ├──────────────┤
         │ Interaction  │  play() functions
         │   Tests      │  (@storybook/test)
         ├──────────────┤
         │  Unit Tests  │  Vitest + storybookTest
         │  (stories)   │  plugin
         └──────────────┘

Each layer catches different defects: unit tests validate logic, interaction tests verify user flows, a11y tests catch accessibility violations, and visual tests catch unintended UI regressions.

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Quick Start

CSF3 Story with Play Function

// Button.stories.tsx
import type { Meta, StoryObj } from '@storybook/react'
import { expect, fn, userEvent, within } from 'storybook/test'
import { Button } from './Button'

const meta = {
  component: Button,
  args: {
    onClick: fn(),
  },
} satisfies Meta<typeof Button>

export default meta
type Story = StoryObj<typeof meta>

export const Primary: Story = {
  args: {
    label: 'Click me',
    variant: 'primary',
  },
  play: async ({ canvasElement, args }) => {
    const canvas = within(canvasElement)
    const button = canvas.getByRole('button', { name: /click me/i })

    await userEvent.click(button)
    await expect(args.onClick).toHaveBeenCalledOnce()
    await expect(button).toHaveStyle({ backgroundColor: 'rgb(37, 99, 235)' })
  },
}

Vitest Configuration

// vitest.config.ts
import { storybookTest } from '@storybook/addon-vitest/vitest-plugin'
import { defineConfig } from 'vitest/config'

export default defineConfig({
  plugins: [storybookTest()],
  test: {
    setupFiles: ['./vitest.setup.ts'],
  },
})

---

Key Principles

• Stories are tests. Every story with a play() function is an executable interaction test that runs in Vitest.
• CSF3 + satisfies for type safety. Use satisfies Meta<typeof Component> for full type inference on args and play functions.
• Module automocking (SB 10). Register sb.mock(import(...)) in .storybook/preview.ts, configure per-story with mocked() in beforeEach. Never use vi.mock in story files. No factory functions — sb.mock is build-time, not runtime.
• TurboSnap for CI speed. Only snapshot stories affected by code changes — reduces Chromatic usage by 60-90%.
• Accessibility is not optional. The a11y addon runs axe-core scans on every story and gates CI on violations.
• Living documentation. Autodocs generates prop tables and usage examples directly from stories — no separate docs site needed.

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Anti-Patterns (FORBIDDEN)

Anti-Pattern	Why It Fails	Use Instead
CSF2 Template.bind({})	Deprecated, no type inference, will be removed in SB 11	CSF3 object stories with satisfies
@storybook/test-runner package	Deprecated since Storybook 9	@storybook/addon-vitest
vi.mock() in story files	Leaks between stories, breaks isolation	Register sb.mock(import(...)) in preview.ts, configure with mocked() in beforeEach
Full Chromatic snapshots on every PR	Expensive and slow	TurboSnap with onlyChanged: true
Manual accessibility checking	Misses violations, not repeatable	@storybook/addon-a11y in CI pipeline
Separate documentation site	Drifts from actual component behavior	Autodocs with tags: ['autodocs']
Testing implementation details	Brittle, breaks on refactors	Test user-visible behavior via play()
CJS imports in stories	ESM-only since SB 9/10	Use ESM imports, set "module": "ESNext" in tsconfig

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Storybook MCP Integration (addon-mcp)

When @storybook/addon-mcp is installed, agents can run tests and preview stories via MCP instead of CLI. This enables the generate → test → self-heal loop.

MCP Tools for Testing

Tool	Purpose
run-story-tests	Run component + a11y tests via MCP, returns pass/fail + violation details
preview-stories	Returns preview URLs for visual verification in chat
get-storybook-story-instructions	Guidance on writing effective stories + interaction tests

Agent Testing Loop

# 1. Generate component + CSF3 story
# 2. Run tests via MCP
results = run-story-tests(
    stories=[{ "storyId": "button--primary" }],
    a11y=True
)
# 3. If failures: read violations, fix, retry (max 3)
# 4. Preview in chat for visual confirmation
preview-stories(stories=[{ "storyId": "button--primary" }])

Setup

npx storybook add @storybook/addon-mcp   # current: 0.6.0, Apr 2026
# Enable docs toolset in .storybook/main.ts:
#   componentsManifest: true    # was experimentalComponentsManifest (SB 10.3 rename, default-on)
npx mcp-add --type http --url "http://localhost:6006/mcp" --scope project

See storybook-mcp-integration skill for full tool reference and patterns.

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References

• references/storybook-migration-guide.md — Migration path from Storybook 9 to 10
• references/storybook-ci-strategy.md — CI pipeline configuration for visual, interaction, and a11y testing
• references/storybook-addon-ecosystem.md — Essential addons for Storybook 10 in 2026

Related Skills

• storybook-mcp-integration — Storybook MCP tools: component discovery, testing, previews
• react-server-components-framework — React 19 + Next.js 16 patterns (component architecture)
• accessibility — Broader accessibility patterns beyond Storybook
• devops-deployment — CI/CD pipeline patterns for automated testing