visual-regression

What this skill does

# Visual Regression Testing Setup Skill

---

## Skill Purpose

Generate complete visual regression testing setup with Storybook stories, configuration files, and CI/CD workflows.

**Supports**: Chromatic, Percy, BackstopJS
**Frameworks**: React, Vue, Svelte (TypeScript/JavaScript)
**CI/CD**: GitHub Actions, GitLab CI, CircleCI

---

## What This Skill Does

1. **Detects existing setup**: Storybook version, VR tool, CI platform
2. **Validates component**: Extract props, variants, states
3. **Generates stories**: Complete `.stories.tsx` with all variants
4. **Creates config files**: Chromatic, Percy, or BackstopJS configuration
5. **Sets up CI/CD**: Auto-generate workflow files
6. **Provides instructions**: Next steps for API tokens, first baseline

---

## Workflow

### Step 1: Validate Project Setup

**Execute**: `vr_setup_validator.py`

**Check**:
- Framework (React/Vue/Svelte) from package.json
- Existing Storybook config (.storybook/ directory)
- Existing VR tool (chromatic, percy, backstopjs in dependencies)
- CI platform (.github/, .gitlab-ci.yml, .circleci/)
- Component file exists and is valid

**Output**:
```json
{
  "framework": "react",
  "storybook_version": "7.6.0",
  "vr_tool": "chromatic",
  "ci_platform": "github",
  "component": {
    "path": "src/components/ProfileCard.tsx",
    "name": "ProfileCard",
    "props": [...],
    "valid": true
  },
  "dependencies": {
    "installed": ["@storybook/react", "@storybook/addon-essentials"],
    "missing": ["chromatic", "@chromatic-com/storybook"]
  }
}
```

**If Storybook not found**: Ask user if they want to install Storybook first, provide setup instructions.

**If multiple VR tools found**: Ask user which to use (Chromatic recommended).

---

### Step 2: Generate Storybook Stories

**Execute**: `story_generator.py`

**Process**:
1. Parse component file (TypeScript/JSX/Vue SFC)
2. Extract props, prop types, default values
3. Identify variants (size, variant, disabled, etc.)
4. Generate story file from template
5. Add accessibility tests (@storybook/addon-a11y)
6. Add interaction tests (if @storybook/test available)

**Template**: `templates/story-template.tsx.j2`

**Example output** (`ProfileCard.stories.tsx`):
```typescript
import type { Meta, StoryObj } from '@storybook/react';
import { ProfileCard } from './ProfileCard';

const meta = {
  title: 'Components/ProfileCard',
  component: ProfileCard,
  parameters: {
    layout: 'centered',
  },
  tags: ['autodocs'],
  argTypes: {
    size: { control: 'select', options: ['sm', 'md', 'lg'] },
    variant: { control: 'select', options: ['default', 'compact'] },
  },
} satisfies Meta<typeof ProfileCard>;

export default meta;
type Story = StoryObj<typeof meta>;

export const Default: Story = {
  args: {
    name: 'John Doe',
    avatar: 'https://example.com/avatar.jpg',
    bio: 'Software Engineer',
    size: 'md',
    variant: 'default',
  },
};

export const Small: Story = {
  args: {
    ...Default.args,
    size: 'sm',
  },
};

export const Large: Story = {
  args: {
    ...Default.args,
    size: 'lg',
  },
};

export const Compact: Story = {
  args: {
    ...Default.args,
    variant: 'compact',
  },
};

// Accessibility test
Default.parameters = {
  a11y: {
    config: {
      rules: [
        { id: 'color-contrast', enabled: true },
        { id: 'label', enabled: true },
      ],
    },
  },
};
```

**Write to**: `{component_directory}/{ComponentName}.stories.tsx`

---

### Step 3: Generate Configuration Files

**Execute**: `chromatic_config_generator.py` (or percy/backstop equivalent)

#### For Chromatic:

**Generate 3 files**:

1. **chromatic.config.json**:
```json
{
  "projectId": "<PROJECT_ID_PLACEHOLDER>",
  "buildScriptName": "build-storybook",
  "exitZeroOnChanges": true,
  "exitOnceUploaded": true,
  "onlyChanged": true,
  "externals": ["public/**"],
  "skip": "dependabot/**",
  "ignoreLastBuildOnBranch": "main"
}
```

2. **Update .storybook/main.js** (add addon):
```javascript
module.exports = {
  stories: ['../src/**/*.stories.@(js|jsx|ts|tsx)'],
  addons: [
    '@storybook/addon-links',
    '@storybook/addon-essentials',
    '@chromatic-com/storybook', // ← Added
    '@storybook/addon-interactions',
  ],
  framework: {
    name: '@storybook/react-vite',
    options: {},
  },
};
```

3. **Update package.json** (add scripts):
```json
{
  "scripts": {
    "chromatic": "npx chromatic",
    "chromatic:ci": "npx chromatic --exit-zero-on-changes"
  }
}
```

**For Percy**: Generate `.percy.yml` instead
**For BackstopJS**: Generate `backstop.config.js` instead

---

### Step 4: Generate CI/CD Workflow

**Execute**: `ci_workflow_generator.py`

**Detect CI platform** from existing files:
- `.github/workflows/` → GitHub Actions
- `.gitlab-ci.yml` → GitLab CI
- `.circleci/config.yml` → CircleCI
- None → Ask user, default to GitHub Actions

#### GitHub Actions Example:

**Generate**: `.github/workflows/chromatic.yml`

```yaml
name: Visual Regression Tests

on:
  push:
    branches: [main, develop]
  pull_request:
    branches: [main]

jobs:
  chromatic:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0 # Required for Chromatic

      - name: Setup Node.js
        uses: actions/setup-node@v4
        with:
          node-version: '20'
          cache: 'npm'

      - name: Install dependencies
        run: npm ci

      - name: Run Chromatic
        uses: chromaui/action@latest
        with:
          projectToken: ${{ secrets.CHROMATIC_PROJECT_TOKEN }}
          exitZeroOnChanges: true
          onlyChanged: true
```

**For GitLab CI**: Add job to `.gitlab-ci.yml`
**For CircleCI**: Add job to `.circleci/config.yml`

---

### Step 5: Provide Setup Instructions

**Output to user**:

````markdown
✅ Visual regression testing setup complete!

## Files Created/Modified

✅ {ComponentName}.stories.tsx (Storybook story with variants)
✅ chromatic.config.json (Chromatic configuration)
✅ .storybook/main.js (Added @chromatic-com/storybook addon)
✅ package.json (Added chromatic scripts)
✅ .github/workflows/chromatic.yml (CI workflow)

## Next Steps

### 1. Install Dependencies

```bash
npm install --save-dev chromatic @chromatic-com/storybook
```

### 2. Create Chromatic Project

1. Go to https://www.chromatic.com/start
2. Sign in with GitHub
3. Create new project
4. Copy project token

### 3. Add Secret to GitHub

1. Go to repository Settings → Secrets and variables → Actions
2. Create secret: `CHROMATIC_PROJECT_TOKEN`
3. Paste your project token

### 4. Update chromatic.config.json

Replace `<PROJECT_ID_PLACEHOLDER>` with your actual project ID from Chromatic dashboard.

### 5. Create Baseline

```bash
npm run chromatic
```

This captures the initial screenshots as your baseline.

### 6. Test Visual Regression

1. Make a visual change to ProfileCard
2. Commit and push
3. CI will run Chromatic automatically
4. Review changes in Chromatic dashboard

## Documentation

See `.agent/sops/testing/visual-regression-setup.md` for detailed workflow.

## Troubleshooting

**Storybook build fails**: Ensure all component dependencies are installed
**Chromatic upload fails**: Check project token in secrets
**No changes detected**: Chromatic only runs on changed stories (use `--force-rebuild` to test)
````

---

## Predefined Functions Reference

### vr_setup_validator.py

```python
def detect_storybook_config(project_root: str) -> dict
def detect_vr_tool(project_root: str) -> str
def validate_component_path(component_path: str) -> dict
def check_dependencies(project_root: str) -> dict
```

**Returns**: Validation report with detected setup and missing dependencies

### story_generator.py

```python
def analyze_component(component_path: str, framework: str) -> dict
def generate_story(component_info: dict, template_path: str) -> str
def create_accessibility_tests(component_info: dict) -> str
def create_interaction_tests(component_info: dict) -> str
```

**Returns**: Generated story file content

### chroma