test-generator

# Test Generator Skill

Auto-suggest tests when you write new code.

## When I Activate

- ✅ New function created
- ✅ New component added
- ✅ User mentions testing or tests
- ✅ Test file missing for implementation
- ✅ User asks "can you test this?"

## What I Generate

### Quick Test Scaffolding
- Basic happy path tests
- Null/undefined edge cases
- Simple error scenarios
- Framework-appropriate syntax (Jest/Vitest/Pytest)

### What I Don't Do
- Comprehensive test suites → Use **@test-engineer** sub-agent
- Integration tests → Use **@test-engineer** sub-agent
- E2E test design → Use **@test-engineer** sub-agent
- Test strategy planning → Use **@test-engineer** sub-agent

## Relationship with @test-engineer Sub-Agent

**Me (Skill):** Quick test scaffolding
**@test-engineer (Sub-Agent):** Comprehensive testing strategy

### Workflow
1. You write a function
2. I auto-generate basic test structure
3. You want full suite → Invoke **@test-engineer** sub-agent
4. Sub-agent creates comprehensive tests

## Examples

### JavaScript Function

```javascript
// You write:
function calculateDiscount(price, percentage) {
  if (price <= 0) throw new Error('Invalid price');
  return price * (percentage / 100);
}

// I auto-generate:
describe('calculateDiscount', () => {
  it('calculates discount correctly', () => {
    expect(calculateDiscount(100, 10)).toBe(10);
  });

  it('throws error for invalid price', () => {
    expect(() => calculateDiscount(0, 10)).toThrow('Invalid price');
  });

  it('handles zero percentage', () => {
    expect(calculateDiscount(100, 0)).toBe(0);
  });

  // TODO: Add more edge cases
  // Consider: negative percentages, decimal values, very large numbers
});
```

### React Component

```jsx
// You write:
function UserCard({ user, onEdit }) {
  return (
    <div className="user-card">
      <h2>{user.name}</h2>
      <button onClick={() => onEdit(user.id)}>Edit</button>
    </div>
  );
}

// I auto-generate:
import { render, screen, fireEvent } from '@testing-library/react';

describe('UserCard', () => {
  const mockUser = { id: 1, name: 'John Doe' };
  const mockOnEdit = jest.fn();

  it('renders user name', () => {
    render(<UserCard user={mockUser} onEdit={mockOnEdit} />);
    expect(screen.getByText('John Doe')).toBeInTheDocument();
  });

  it('calls onEdit with user id when button clicked', () => {
    render(<UserCard user={mockUser} onEdit={mockOnEdit} />);
    fireEvent.click(screen.getByText('Edit'));
    expect(mockOnEdit).toHaveBeenCalledWith(1);
  });

  // TODO: Add tests for edge cases
  // - Missing user data
  // - Undefined onEdit
  // - Long names (UI testing)
});
```

### Python Function

```python
# You write:
def fetch_user_data(user_id: int) -> dict:
    if user_id <= 0:
        raise ValueError("Invalid user ID")
    return db.query("SELECT * FROM users WHERE id = ?", [user_id])

# I auto-generate:
import pytest

def test_fetch_user_data_success():
    """Test successful user data retrieval"""
    result = fetch_user_data(1)
    assert isinstance(result, dict)
    assert 'id' in result

def test_fetch_user_data_invalid_id():
    """Test with invalid user ID"""
    with pytest.raises(ValueError, match="Invalid user ID"):
        fetch_user_data(0)

def test_fetch_user_data_negative_id():
    """Test with negative ID"""
    with pytest.raises(ValueError):
        fetch_user_data(-1)

# TODO: Add integration tests with database
# TODO: Test database connection failures
```

## Framework Detection

I automatically detect your testing framework:

- **JavaScript/TypeScript**: Jest, Vitest, Mocha
- **Python**: pytest, unittest
- **Java**: JUnit
- **Go**: testing package

Detection based on:
- package.json dependencies
- requirements.txt
- Existing test files
- Import statements

## Test Patterns

### Unit Tests
```javascript
// Function testing
test('adds numbers correctly', () => {
  expect(add(2, 3)).toBe(5);
});
```

### Component Tests
```jsx
// React component testing
test('button click triggers callback', () => {
  const onClick = jest.fn();
  render(<Button onClick={onClick} />);
  fireEvent.click(screen.getByRole('button'));
  expect(onClick).toHaveBeenCalled();
});
```

### Edge Cases
```javascript
// Boundary testing
test('handles empty input', () => {
  expect(processData([])).toEqual([]);
});

test('handles null input', () => {
  expect(processData(null)).toBeNull();
});
```

## When to Use Sub-Agent

Invoke **@test-engineer** for:
- Complete test suites (20+ tests)
- Integration test strategy
- E2E test planning
- Test coverage goals
- Complex mocking scenarios

**Example:**
```
Me: "Generated 3 basic tests for calculateDiscount()"
You: "@test-engineer create comprehensive test suite with all edge cases"
Sub-agent: [Creates 25+ tests covering all scenarios]
```

## Sandboxing Compatibility

**Works without sandboxing:** ✅ Yes
**Works with sandboxing:** ✅ Yes

- **Filesystem**: Writes test files to project
- **Network**: None required
- **Configuration**: None required

## Customization

Edit test templates:

```bash
cp -r ~/.claude/skills/development/test-generator \
      ~/.claude/skills/development/my-test-generator

# Edit SKILL.md to customize:
# - Test patterns
# - Framework preferences
# - Coverage expectations
```

## Integration with Commands

### /test-gen Command
```bash
/test-gen --file utils.js --framework jest --coverage 90

# Combines:
# 1. My quick scaffolding
# 2. @test-engineer comprehensive tests
# 3. Full test file generation
```

## Tips

1. **Let me scaffold first** - Review before invoking sub-agent
2. **Add TODOs** - I include TODO comments for complex cases
3. **Framework consistency** - I match your project's testing style
4. **Quick iteration** - Regenerate if not satisfied

## Related Tools

- **@test-engineer**: Comprehensive test suite creation
- **code-reviewer skill**: Flags code that needs testing
- **/test-gen command**: Full test generation workflow