Unit Test Generation Skill

Generate comprehensive unit tests for any source code with a target of 100% coverage.

When to Use

This skill activates when:

• User asks for unit tests for a file or component
• Code needs test coverage
• User mentions "test", "coverage", "jest", "vitest"
• After writing new code that needs testing

Supported File Types

• React components (.tsx, .jsx)
• Utility functions (.ts, .js)
• Custom hooks (use*.ts, use*.tsx)
• API routes (route.ts, api/*.ts)
• Classes and modules

Test Generation Process

1. Analyze the source file:

   • Identify exported functions, components, hooks
   • Map conditional branches and logic paths
   • Note dependencies and imports

2. Generate test cases for:

   • Happy path scenarios
   • Edge cases (empty, null, boundary)
   • Error handling paths
   • All branches and conditions

3. Write test code following patterns:

   • Use React Testing Library for components
   • Mock external dependencies
   • Use descriptive test names
   • Group with describe blocks

Test File Template

import { render, screen, fireEvent } from '@testing-library/react';
import { ComponentName } from './ComponentName';

describe('ComponentName', () => {
  describe('rendering', () => {
    it('should render correctly with default props', () => {
      render(<ComponentName />);
      expect(screen.getByRole('...')).toBeInTheDocument();
    });
  });

  describe('interactions', () => {
    it('should handle click events', () => {
      const onClick = jest.fn();
      render(<ComponentName onClick={onClick} />);
      fireEvent.click(screen.getByRole('button'));
      expect(onClick).toHaveBeenCalled();
    });
  });

  describe('edge cases', () => {
    it('should handle empty props gracefully', () => {
      render(<ComponentName items={[]} />);
      expect(screen.getByText('No items')).toBeInTheDocument();
    });
  });
});

Best Practices

• Test behavior, not implementation
• Use meaningful test descriptions
• Keep tests independent and isolated
• Mock external services and APIs
• Test accessibility where applicable
• Aim for 100% branch coverage
• Follow AAA pattern (Arrange, Act, Assert)