Storybook Testing

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

---

Quick Reference

---

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.

---

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.

---

Anti-Patterns (FORBIDDEN)

---

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

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.

---

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

Storybook Addon Ecosystem (2026)

Overview

Storybook 10 consolidates its addon ecosystem around first-party addons. Essential addons (viewport, controls, interactions, actions) are now bundled in core — remove them as separate dependencies. Testing utilities are unified under storybook/test.

---

Essential Addons

Testing & Quality

UI & Design

Documentation

External Services

---

Recommended .storybook/main.ts Configuration

import type { StorybookConfig } from '@storybook/react-vite'

const config: StorybookConfig = {
  stories: ['../src/**/*.stories.@(ts|tsx)'],
  addons: [
    '@storybook/addon-vitest',
    '@storybook/addon-a11y',
    '@storybook/addon-interactions',
    '@storybook/addon-themes',
    '@storybook/addon-viewport',
  ],
  framework: '@storybook/react-vite',
  docs: {
    autodocs: 'tag',  // generate docs for stories with 'autodocs' tag
  },
}

export default config

---

Deprecated / Removed

---

Version Compatibility

• Storybook 10: React 18+, Vue 3.5+, Angular 18+, Svelte 5+
• Node.js: 20.16+ / 22.19+ / 24+ required (ESM-only)
• Bundler: Vite 8 recommended, Webpack 5 supported
• Vitest: 4.1+ supported

Storybook CI Strategy (Storybook 10)

Overview

A complete Storybook 10 CI pipeline combines three layers: Vitest 4.1+ for interaction tests, Chromatic for visual regression, and addon-a11y for accessibility — all running in parallel for fast feedback.

---

Pipeline Architecture

PR opened
├── Vitest (interaction + smoke)     ~2 min
│   ├── Stories with play() → interaction tests
│   ├── Stories without play() → smoke tests (render without error)
│   └── a11y addon → accessibility violations fail tests
├── Chromatic (visual regression)    ~3 min with TurboSnap
│   ├── TurboSnap → only changed stories snapshotted
│   ├── Visual diff review in Chromatic UI
│   └── Auto-accept on dependabot/renovate PRs
└── Lint + Type Check                ~1 min
    ├── ESLint with storybook plugin
    └── tsc --noEmit

---

GitHub Actions Workflow

name: Storybook CI
on:
  pull_request:
    branches: [main]

jobs:
  interaction-tests:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with: { node-version: 22 }
      - run: npm ci
      - run: npx vitest --project=storybook --reporter=junit --outputFile=results.xml
      - uses: actions/upload-artifact@v4
        if: failure()
        with:
          name: test-results
          path: results.xml

  visual-regression:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with: { fetch-depth: 0 }
      - uses: actions/setup-node@v4
        with: { node-version: 22 }
      - run: npm ci
      - uses: chromaui/action@latest
        with:
          projectToken: ${{ secrets.CHROMATIC_PROJECT_TOKEN }}
          onlyChanged: true
          externals: |
            - 'src/styles/**'
            - 'public/fonts/**'

  a11y-audit:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with: { node-version: 22 }
      - run: npm ci
      - run: npx vitest --project=storybook --reporter=default
        env:
          STORYBOOK_A11Y_STRICT: 'true'

---

TurboSnap Cost Optimization

---

Best Practices

• Run Vitest interaction tests and Chromatic visual regression in parallel — they are independent.
• Use onlyChanged: true for TurboSnap to minimize Chromatic snapshot costs.
• Set STORYBOOK_A11Y_STRICT=true in CI to fail on any a11y violation (non-strict mode only warns).
• Cache node_modules and .storybook/cache between CI runs for faster builds.
• Use --reporter=junit for Vitest to produce CI-compatible test reports.
• Auto-accept Chromatic changes on bot PRs (Dependabot, Renovate) to avoid blocking dependency updates.

Storybook Migration Guide

Storybook 9 → 10 (Current)

Breaking Changes in Storybook 10

1. CSF2 Deprecated (Still Works)

CSF2 Template.bind({}) still works in SB 10 for backwards compatibility, but is deprecated and will be removed in SB 11. Migrate to CSF3 object format:

// CSF3 (recommended)
export const Primary: Story = {
  args: { label: 'Click me' },
}

Run the codemod to migrate:

npx storybook@latest migrate csf-2-to-3 --glob="src/**/*.stories.tsx"

2. ESM-Only Enforced

All Storybook packages are ESM-only. Ensure your tsconfig.json is configured:

{
  "compilerOptions": {
    "module": "ESNext",
    "moduleResolution": "bundler"
  }
}

3. Module Automocking

Storybook 10 introduces automatic module mocking. For explicit per-story overrides, use the two-part pattern:

1. Register mocks in .storybook/preview.ts:

import { sb } from '@storybook/test'
sb.mock(import('../src/api/client'), { spy: true })

2. Configure per-story with mocked() in beforeEach:

import { mocked } from '@storybook/test'
import { fetchUser } from '../src/api/client'

export const WithUser: Story = {
  beforeEach: () => {
    mocked(fetchUser).mockResolvedValue({ id: '1', name: 'Test' })
  },
}

4. React Server Component Support

Stories can now render React Server Components in isolation:

import type { Meta, StoryObj } from '@storybook/react'
import { ServerComponent } from './ServerComponent'

const meta = {
  component: ServerComponent,
  // RSC stories work without additional configuration in SB 10
} satisfies Meta<typeof ServerComponent>

5. Parallel Browser Tests

Vitest integration now runs stories in parallel browser contexts for faster CI:

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

export default defineConfig({
  plugins: [storybookTest({ parallel: true })],
})

Migration Steps

# 1. Upgrade
npx storybook@latest upgrade

# 2. Run codemods (handles most breaking changes)
npx storybook@latest automigrate

# 3. Verify
npm run storybook        # visual check
npx vitest               # run story tests
npx chromatic            # visual regression baseline

---

Storybook 7/8 → 9 (Legacy)

Breaking Changes in Storybook 9

1. ESM-Only Packages

All Storybook packages became ESM-only.

2. CSF3 is Default

CSF2 still works but deprecated.

3. Test Runner Replaced by Vitest Addon

npm uninstall @storybook/test-runner
npm install -D @storybook/addon-vitest

4. Module Mocking: vi.mock → sb.mock

Two-part pattern: register in preview.ts, configure per-story.

5. Actions: action() → fn()

// Before
import { action } from '@storybook/addon-actions'
args: { onClick: action('clicked') }

// After
import { fn } from '@storybook/test'
args: { onClick: fn() }

6. Unified Imports

// Before (scattered imports)
import { action } from '@storybook/addon-actions'
import { within, userEvent } from '@storybook/testing-library'

// After (unified under @storybook/test)
import { fn, within, userEvent, expect } from '@storybook/test'

Rule Categories

1. Story Authoring (storybook) — HIGH/MEDIUM — 2 rules

Typesafe story creation and automated documentation generation.

• storybook-csf3-factories.md — Typesafe CSF3 story factories with satisfies Meta<typeof Component>
• storybook-autodocs.md — Auto-generated documentation from stories with autodocs tag

2. Interaction Testing (storybook) — CRITICAL/HIGH — 2 rules

User interaction simulation and story-as-test execution via Vitest.

• storybook-play-functions.md — Interaction testing with play() functions and @storybook/test
• storybook-vitest-integration.md — Run stories as Vitest tests via @storybook/addon-vitest

3. Visual Regression (storybook) — HIGH — 1 rule

Automated visual diff testing with optimized snapshot strategies.

• storybook-chromatic-turbosnap.md — TurboSnap reduces Chromatic snapshot usage by 60-90%

4. Isolation & Mocking (storybook) — HIGH — 1 rule

Story-level module mocking for deterministic tests.

• storybook-sb-mock.md — sb.mock for story-level module isolation replaces vi.mock

5. Accessibility (storybook) — CRITICAL — 1 rule

Automated accessibility validation integrated into the testing pipeline.

• storybook-a11y-testing.md — Accessibility testing with @storybook/addon-a11y and axe-core in CI

[Rule Name]

[Brief description — 1-2 sentences.]

Incorrect:

// Bad pattern

Correct:

// Good pattern

Key rules:

• [Rule 1]
• [Rule 2]
• [Rule 3]

Reference: [link]

Storybook: Accessibility Testing with addon-a11y

The @storybook/addon-a11y addon runs axe-core scans on every story, surfacing WCAG violations in the Storybook panel and failing CI pipelines. In Storybook 10, a11y checks integrate directly with the Vitest addon — accessibility violations become test failures.

Incorrect:

// Manual accessibility checking — unreliable and not repeatable
import type { Meta, StoryObj } from '@storybook/react'
import { Button } from './Button'

const meta = { component: Button } satisfies Meta<typeof Button>
export default meta
type Story = StoryObj<typeof meta>

export const IconOnly: Story = {
  args: {
    icon: <SearchIcon />,
    // No aria-label — screen readers cannot identify the button
    // No automated test catches this
  },
}

Correct:

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

const meta = {
  component: Button,
  tags: ['autodocs'],
  parameters: {
    a11y: {
      config: {
        rules: [
          { id: 'color-contrast', enabled: true },
          { id: 'button-name', enabled: true },
        ],
      },
    },
  },
} satisfies Meta<typeof Button>

export default meta
type Story = StoryObj<typeof meta>

export const IconOnly: Story = {
  args: {
    icon: <SearchIcon />,
    'aria-label': 'Search',  // accessible name for icon-only button
  },
  play: async ({ canvasElement }) => {
    const canvas = within(canvasElement)
    const button = canvas.getByRole('button', { name: /search/i })
    await expect(button).toBeVisible()
    await expect(button).toHaveAccessibleName('Search')
  },
}

export const DisabledState: Story = {
  args: {
    label: 'Submit',
    disabled: true,
  },
  play: async ({ canvasElement }) => {
    const canvas = within(canvasElement)
    const button = canvas.getByRole('button', { name: /submit/i })
    await expect(button).toBeDisabled()
    // a11y addon automatically checks contrast, ARIA, focus management
  },
}

// .storybook/main.ts — register a11y addon
const config: StorybookConfig = {
  addons: [
    '@storybook/addon-vitest',
    '@storybook/addon-a11y',  // runs axe-core on every story
  ],
}

Key rules:

• Add @storybook/addon-a11y to your Storybook addons — it runs axe-core scans on every story render.
• A11y violations appear in the Storybook panel AND fail as Vitest test assertions in CI.
• Configure rules per-story via parameters.a11y.config.rules to enable/disable specific axe rules.
• Use tags: ['!a11y'] to exclude specific stories from a11y checks (e.g., intentional error states).
• Always provide accessible names: aria-label for icon buttons, <label> for inputs, headings for sections.
• Test keyboard navigation in play functions: userEvent.tab(), userEvent.keyboard('{Enter}').

Reference: references/storybook-ci-strategy.md

Storybook: Autodocs for Living Documentation

Storybook 10 generates documentation pages automatically from stories tagged with autodocs. Prop tables are derived from TypeScript types, code examples from story definitions, and usage descriptions from JSDoc comments. No separate documentation tool needed.

Incorrect:

// Separate documentation maintained manually — drifts from reality
// docs/components/Button.mdx
import { Button } from '../components/Button'

# Button

| Prop | Type | Default |
|------|------|---------|
| label | string | — |
| variant | 'primary' \| 'secondary' | 'primary' |
| size | 'sm' \| 'md' \| 'lg' | 'md' |

// ^ This table is manually maintained and already out of date
// The component added a 'danger' variant last sprint

Correct:

// Button.stories.tsx — autodocs generates the docs page
import type { Meta, StoryObj } from '@storybook/react'
import { fn } from 'storybook/test'
import { Button } from './Button'

const meta = {
  component: Button,
  tags: ['autodocs'],  // generates a Docs page for this component
  args: {
    onClick: fn(),
  },
  argTypes: {
    variant: {
      control: 'select',
      options: ['primary', 'secondary', 'danger'],
      description: 'Visual style variant of the button',
      table: { defaultValue: { summary: 'primary' } },
    },
    size: {
      control: 'radio',
      options: ['sm', 'md', 'lg'],
      description: 'Button size affecting padding and font size',
      table: { defaultValue: { summary: 'md' } },
    },
  },
} satisfies Meta<typeof Button>

export default meta
type Story = StoryObj<typeof meta>

/** The default button style used for primary actions. */
export const Primary: Story = {
  args: { label: 'Click me', variant: 'primary' },
}

/** Secondary button for less prominent actions. */
export const Secondary: Story = {
  args: { label: 'Cancel', variant: 'secondary' },
}

/** Danger variant for destructive actions like delete. */
export const Danger: Story = {
  args: { label: 'Delete', variant: 'danger' },
}

// Button.tsx — JSDoc comments appear in autodocs
interface ButtonProps {
  /** Text displayed inside the button */
  label: string
  /** Visual style variant */
  variant?: 'primary' | 'secondary' | 'danger'
  /** Button size affecting padding and font size */
  size?: 'sm' | 'md' | 'lg'
  /** Click handler */
  onClick?: () => void
}

Key rules:

• Add tags: ['autodocs'] to the meta object — this generates a Docs page for the component.
• Use argTypes with description and table.defaultValue for rich prop documentation.
• Add JSDoc comments to component props — autodocs extracts them for the prop table.
• Add JSDoc comments to story exports — they appear as descriptions on the docs page.
• To enable autodocs globally, set tags: ['autodocs'] in .storybook/preview.ts.
• Use parameters.docs.description.component for a component-level description at the top of the docs page.

Reference: references/storybook-addon-ecosystem.md

Storybook: Chromatic TurboSnap

Chromatic TurboSnap uses Webpack/Vite dependency graphs to identify which stories are affected by code changes in a PR. Only affected stories are snapshotted, reducing Chromatic usage by 60-90% and speeding up visual regression checks.

Incorrect:

# .github/workflows/chromatic.yml — full snapshots every time
name: Chromatic
on: pull_request
jobs:
  chromatic:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0
      - uses: chromaui/action@latest
        with:
          projectToken: ${{ secrets.CHROMATIC_PROJECT_TOKEN }}
          # No TurboSnap — snapshots ALL stories on every PR
          # 500 stories × 3 viewports = 1500 snapshots per PR

Correct:

# .github/workflows/chromatic.yml — TurboSnap enabled
name: Chromatic
on: pull_request
jobs:
  chromatic:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0  # required for TurboSnap git comparison
      - uses: chromaui/action@latest
        with:
          projectToken: ${{ secrets.CHROMATIC_PROJECT_TOKEN }}
          onlyChanged: true  # enable TurboSnap
          externals: |
            - 'src/styles/**'
            - 'public/fonts/**'
          traceChanged: 'expanded'
          skip: 'dependabot/**'

// .storybook/main.ts — ensure correct build for TurboSnap
const config: StorybookConfig = {
  stories: ['../src/**/*.stories.@(ts|tsx)'],
  framework: '@storybook/react-vite',
  // TurboSnap works automatically with Vite's module graph
}

Key rules:

• Set onlyChanged: true in the Chromatic GitHub Action to enable TurboSnap.
• Use fetch-depth: 0 in checkout — TurboSnap needs full git history to compare changes.
• Declare externals for files outside the module graph (global CSS, fonts, static assets) so changes to them trigger relevant snapshots.
• Use traceChanged: 'expanded' to trace transitive dependencies (a utility change affects all stories that import it).
• Set skip for bot branches (Dependabot, Renovate) to avoid wasting snapshots on automated PRs.
• TurboSnap works with both Webpack and Vite — no extra configuration needed for Vite-based Storybook.

Reference: references/storybook-ci-strategy.md

Storybook: CSF3 Typesafe Story Factories

Storybook 10 uses Component Story Format 3 (CSF3) where stories are plain objects instead of template-bound functions. Use satisfies Meta<typeof Component> on the meta export for full TypeScript inference on args, decorators, and play functions.

Incorrect:

// CSF2 pattern — no type inference, verbose
import { ComponentStory, ComponentMeta } from '@storybook/react'
import { Button } from './Button'

export default {
  title: 'Components/Button',
  component: Button,
} as ComponentMeta<typeof Button>

const Template: ComponentStory<typeof Button> = (args) => <Button {...args} />

export const Primary = Template.bind({})
Primary.args = {
  label: 'Click me',
  variant: 'primary',
  onClck: () => {},  // typo not caught — no type checking on args
}

Correct:

// CSF3 pattern — full type inference via satisfies
import type { Meta, StoryObj } from '@storybook/react'
import { fn } from 'storybook/test'
import { Button } from './Button'

const meta = {
  component: Button,
  args: {
    onClick: fn(),  // fn() provides mock tracking
  },
  argTypes: {
    variant: {
      control: 'select',
      options: ['primary', 'secondary', 'danger'],
    },
  },
} satisfies Meta<typeof Button>

export default meta
type Story = StoryObj<typeof meta>

export const Primary: Story = {
  args: {
    label: 'Click me',
    variant: 'primary',
    // onClck: () => {},  // TypeScript ERROR — catches typo at compile time
  },
}

export const Secondary: Story = {
  args: {
    label: 'Cancel',
    variant: 'secondary',
  },
}

export const WithLongLabel: Story = {
  args: {
    label: 'This is a button with a very long label to test overflow',
    variant: 'primary',
  },
}

Key rules:

• Always use satisfies Meta<typeof Component> (not as Meta) — satisfies preserves the inferred type while as erases it.
• Define type Story = StoryObj<typeof meta> after the default export for per-story type inference.
• Use fn() from @storybook/test for action args instead of action() — fn() integrates with Vitest assertions.
• Remove title from meta — Storybook 9 auto-generates titles from file paths.
• Each story is a plain object with args, not a function bound via Template.bind({}).

Reference: references/storybook-migration-guide.md

Storybook: Play Functions for Interaction Testing

Every story that demonstrates interactive behavior should include a play() function. Play functions simulate real user interactions using userEvent and validate outcomes with expect — all from @storybook/test. These run automatically in the Storybook UI and as Vitest tests in CI.

Incorrect:

// No play function — behavior is only verified by opening Storybook and clicking manually
import type { Meta, StoryObj } from '@storybook/react'
import { LoginForm } from './LoginForm'

const meta = { component: LoginForm } satisfies Meta<typeof LoginForm>
export default meta
type Story = StoryObj<typeof meta>

export const SubmitForm: Story = {
  args: {
    onSubmit: () => console.log('submitted'),  // no mock tracking
  },
  // No play function — manual testing only
}

Correct:

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

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

export default meta
type Story = StoryObj<typeof meta>

export const SubmitForm: Story = {
  play: async ({ canvasElement, args }) => {
    const canvas = within(canvasElement)

    // Simulate user filling out the form
    await userEvent.type(canvas.getByLabelText(/email/i), 'user@example.com')
    await userEvent.type(canvas.getByLabelText(/password/i), 'SecureP@ss1')
    await userEvent.click(canvas.getByRole('button', { name: /sign in/i }))

    // Assert the callback was called with form data
    await expect(args.onSubmit).toHaveBeenCalledWith({
      email: 'user@example.com',
      password: 'SecureP@ss1',
    })
  },
}

export const ValidationError: Story = {
  play: async ({ canvasElement }) => {
    const canvas = within(canvasElement)

    // Submit empty form
    await userEvent.click(canvas.getByRole('button', { name: /sign in/i }))

    // Assert validation messages appear
    await expect(canvas.getByText(/email is required/i)).toBeVisible()
    await expect(canvas.getByText(/password is required/i)).toBeVisible()
  },
}

Key rules:

• Import expect, fn, userEvent, and within from @storybook/test — not from Vitest or Testing Library directly.
• Use within(canvasElement) to scope queries to the story's rendered output, not screen.
• Use accessible queries: getByRole, getByLabelText, getByText — avoid getByTestId unless no semantic alternative exists.
• Always await each userEvent and expect call — play functions are async.
• Use fn() for callback props so assertions like toHaveBeenCalledWith work correctly.
• Play functions run in sequence: the Storybook UI shows step-by-step results, and Vitest reports pass/fail.

Reference: references/storybook-ci-strategy.md

Storybook: sb.mock for Story-Level Isolation

Storybook 10 provides sb.mock() for module mocking with story-level isolation. It uses a two-part pattern: register mocks in .storybook/preview.ts, then configure per-story behavior using the mocked() utility in beforeEach. Unlike vi.mock(), which leaks between test files, sb.mock is automatically cleaned up between stories.

Incorrect:

// Using vi.mock — leaks between stories, breaks isolation
import type { Meta, StoryObj } from '@storybook/react'
import { vi } from 'vitest'
import { UserProfile } from './UserProfile'

// This mock leaks to ALL stories in this file and potentially others
vi.mock('@/lib/api', () => ({
  fetchUser: vi.fn().mockResolvedValue({ name: 'John', role: 'admin' }),
}))

const meta = { component: UserProfile } satisfies Meta<typeof UserProfile>
export default meta
type Story = StoryObj<typeof meta>

export const AdminUser: Story = {}
export const RegularUser: Story = {}  // Still sees admin mock — no isolation

Correct — Step 1: Register mocks in `.storybook/preview.ts`:

// .storybook/preview.ts — registration only, runs once at startup
import { sb } from '@storybook/test'

// Register modules to mock — use dynamic import(), not string paths
sb.mock(import('../src/lib/api'))

Correct — Step 2: Configure per-story in `beforeEach` using `mocked()`:

// UserProfile.stories.tsx
import type { Meta, StoryObj } from '@storybook/react'
import { expect, mocked, within } from '@storybook/test'
import { UserProfile } from './UserProfile'
import { fetchUser } from '@/lib/api'

const meta = {
  component: UserProfile,
} satisfies Meta<typeof UserProfile>

export default meta
type Story = StoryObj<typeof meta>

export const AdminUser: Story = {
  async beforeEach() {
    // mocked() accesses the spy registered in preview.ts
    mocked(fetchUser).mockResolvedValue({ name: 'John', role: 'admin' })
  },
  play: async ({ canvasElement }) => {
    const canvas = within(canvasElement)
    await expect(canvas.getByText('Admin')).toBeVisible()
  },
}

export const RegularUser: Story = {
  async beforeEach() {
    mocked(fetchUser).mockResolvedValue({ name: 'Jane', role: 'user' })
  },
  play: async ({ canvasElement }) => {
    const canvas = within(canvasElement)
    await expect(canvas.getByText('User')).toBeVisible()
  },
}

Key rules:

• Register mocks in .storybook/preview.ts using sb.mock(import(...)) — this is the only place sb.mock can be called.
• Configure per-story using mocked(namedExport).mockResolvedValue(...) in beforeEach — never call sb.mock() in story files.
• sb.mock uses import() expressions (not string paths) for module resolution.
• Mocks are automatically restored between stories — no manual cleanup needed.
• Never use vi.mock() at the top level of story files — it leaks across stories and test runs.
• For shared mock setups across multiple stories, define beforeEach on the meta object.

Reference: https://storybook.js.org/docs/writing-stories/mocking-data-and-modules/mocking-modules

Storybook: Vitest Integration

Storybook 9 replaces @storybook/test-runner with @storybook/addon-vitest. Stories run as native Vitest tests — no running Storybook dev server required. The storybookTest Vitest plugin discovers .stories.tsx files and executes their play() functions as test cases.

Incorrect:

// Using deprecated test-runner — requires running Storybook server
// package.json
{
  "scripts": {
    "test-storybook": "test-storybook --url http://localhost:6006"
  },
  "devDependencies": {
    "@storybook/test-runner": "^0.17.0"  // deprecated in Storybook 9
  }
}

// Separate test config for Storybook — duplication
// test-runner-jest.config.js
module.exports = {
  testMatch: ['**/*.stories.*'],
  transform: { /* separate transform config */ },
}

Correct:

// vitest.config.ts — stories run as native Vitest tests
import { storybookTest } from '@storybook/addon-vitest/vitest-plugin'
import { defineConfig } from 'vitest/config'

export default defineConfig({
  plugins: [storybookTest()],
  test: {
    setupFiles: ['./vitest.setup.ts'],
    browser: {
      enabled: true,
      provider: 'playwright',
      instances: [{ browser: 'chromium' }],
    },
  },
})

// .storybook/main.ts — register the addon
import type { StorybookConfig } from '@storybook/react-vite'

const config: StorybookConfig = {
  stories: ['../src/**/*.stories.@(ts|tsx)'],
  addons: [
    '@storybook/addon-vitest',
    '@storybook/addon-a11y',
  ],
  framework: '@storybook/react-vite',
}

export default config

// vitest.setup.ts — global setup for story tests
import '@testing-library/jest-dom/vitest'

Key rules:

• Install @storybook/addon-vitest and remove @storybook/test-runner from dependencies.
• Add storybookTest() to your Vitest config plugins — it auto-discovers .stories.tsx files.
• Stories without play() functions still run as smoke tests (render without errors).
• Use browser mode with Playwright for accurate DOM testing — stories render in a real browser.
• Run vitest to execute both regular tests and story tests in a single command.
• The addon respects tags filtering — use tags: ['!test'] to exclude stories from test runs.

Reference: references/storybook-ci-strategy.md