Jest Test Scaffolder

Jest Test Scaffolder Workflow

This skill creates comprehensive unit tests for React components using Jest, React Testing Library, and user-event.

Workflow Steps

1. Identify component to test:

   • Ask for component file path (e.g., src/components/ui/Button/Button.tsx)
   • Read component file to extract:
     • Component name
     • Props interface/types
     • Event handlers
     • Component role (button, input, form, etc.)
   • Determine test location: {{COMPONENT_DIR}}/__tests__/{{COMPONENT_NAME}}.test.tsx

2. Analyze component structure:

   • Extract prop names and types from TypeScript interface
   • Identify event handlers (onClick, onChange, onSubmit, etc.)
   • Determine accessibility role (button, textbox, combobox, etc.)
   • Identify state variations (disabled, loading, error, etc.)
   • Check for conditional rendering

3. Generate test file:

   • Read template: .claude/skills/jest-test-scaffolder/templates/component.test.tsx.tpl
   • Replace placeholders:
     • {{COMPONENT_NAME}} - Component name (PascalCase)
     • {{COMPONENT_PATH}} - Relative import path
     • {{COMPONENT_ROLE}} - Accessibility role (button, textbox, etc.)
     • {{DEFAULT_PROPS}} - Default props for rendering
     • {{EVENT_HANDLERS}} - Event handler tests
     • {{STATE_TESTS}} - State variation tests (disabled, loading, etc.)
   • Write to: {{COMPONENT_DIR}}/__tests__/{{COMPONENT_NAME}}.test.tsx

4. Include comprehensive test scenarios:

   • ✅ Render Test: Component renders without errors
   • ✅ Props Test: Component accepts and displays props correctly
   • ✅ Interaction Test: User interactions trigger expected behavior
   • ✅ State Test: Component handles state changes (disabled, loading, etc.)
   • ✅ Accessibility Test: Component is accessible (role, labels)
   • ⚠️ Edge Cases: Empty props, long text, null values (TODO placeholders)
   • ⚠️ Snapshot Test: Visual regression (TODO placeholder)

5. Use React Testing Library best practices:

   • Use screen queries (getByRole, getByText, getByLabelText)
   • Use userEvent for realistic interactions
   • Use jest.fn() for Jest mocks
   • Avoid implementation details (no enzyme shallow rendering)
   • Test accessibility (roles, labels, keyboard navigation)

6. Report success:

   • Show test file path
   • Display test coverage (number of test cases)
   • Provide command to run tests: yarn test {{COMPONENT_NAME}}
   • Remind user to add edge case tests

For React Hooks

When testing custom React hooks:

1. Use template: .claude/skills/jest-test-scaffolder/templates/hook.test.tsx.tpl
2. Use @testing-library/react renderHook:

   import { renderHook, act } from "@testing-library/react";
   import { useCustomHook } from "./useCustomHook";
   

3. Test hook behavior:
   • Initial state
   • State updates via act()
   • Return values
   • Side effects

Template Structure

import { render, screen } from '@testing-library/react';
import userEvent from '@testing-library/user-event';
import { jest } from '@jest/globals';
import { {{COMPONENT_NAME}} } from './{{COMPONENT_NAME}}';

describe('{{COMPONENT_NAME}}', () => {
  it('renders without errors', () => {
    render(<{{COMPONENT_NAME}} {{DEFAULT_PROPS}} />);
    expect(screen.getByRole('{{ROLE}}')).toBeInTheDocument();
  });

  it('handles user interactions', async () => {
    const user = userEvent.setup();
    const mock{{HANDLER}} = jest.fn();
    render(<{{COMPONENT_NAME}} on{{HANDLER}}={mock{{HANDLER}}} />);

    await user.click(screen.getByRole('{{ROLE}}'));
    expect(mock{{HANDLER}}).toHaveBeenCalledTimes(1);
  });

  it('handles disabled state', async () => {
    const user = userEvent.setup();
    const mockHandler = jest.fn();
    render(<{{COMPONENT_NAME}} disabled on{{HANDLER}}={mockHandler} />);

    const element = screen.getByRole('{{ROLE}}');
    expect(element).toBeDisabled();

    await user.click(element);
    expect(mockHandler).not.toHaveBeenCalled();
  });

  // TODO: Add accessibility tests
  // TODO: Add snapshot tests
  // TODO: Add edge case tests (empty props, long text, null values)
});

Example Usage

User: "Create tests for the Button component"

Claude (using jest-test-scaffolder):
1. Reads src/components/ui/Button/Button.tsx
2. Extracts props: { children, onClick, disabled, variant, size }
3. Generates src/components/ui/Button/__tests__/Button.test.tsx
4. Creates 5 test cases:
   - Renders with correct text
   - Calls onClick handler when clicked
   - Is disabled when disabled prop is true
   - Renders correct variant styles (TODO)
   - Handles different sizes (TODO)

Files created:
- src/components/ui/Button/__tests__/Button.test.tsx (42 lines, 3 complete tests, 2 TODO tests)

Run tests:
yarn test Button

Test coverage:
✅ Render test
✅ Click interaction test
✅ Disabled state test
⚠️ Variant test (TODO)
⚠️ Size test (TODO)

Pattern Matching

This skill follows the existing test pattern from:

• src/components/ui/Button/__tests__/Button.test.tsx (36 lines, 3 tests)
• Uses describe and it blocks
• Uses screen.getByRole for queries
• Uses userEvent.setup() and await user.click()
• Uses jest.fn() for Jest mocks
• Tests rendering, interactions, and state

Best Practices

1. Test user behavior, not implementation:

   • Query by role, label, text (user-visible)
   • Avoid querying by class names or test IDs (unless necessary)
   • Test what users see and do

2. Use userEvent over fireEvent:

   • More realistic user interactions
   • Handles complex interactions (hover, tab, type)
   • Follows browser behavior

3. Keep tests simple and focused:

   • One assertion per test (when possible)
   • Clear test descriptions
   • Avoid complex setup

4. Test accessibility:

   • Use semantic roles
   • Verify labels and descriptions
   • Test keyboard navigation

5. Mock external dependencies:

   • Mock API calls
   • Mock context providers
   • Mock navigation (useNavigate, useRouter)

Jest vs Vitest

This skill uses Jest (not Vitest):

• jest.fn() instead of vi.fn()
• jest.mock() instead of vi.mock()
• jest.spyOn() instead of vi.spyOn()
• Everything else is the same (React Testing Library patterns)

When NOT to Use This Skill

• ❌ E2E tests → Use webapp-testing skill (Playwright)
• ❌ Integration tests → Use api-integration-test-scaffolder
• ❌ Backend tests → Use pytest-test-scaffolder
• ❌ Storybook stories → Use storybook-scaffolder