mock-generator

What this skill does

# Mock Generator

Automatically generates test mocks, stubs, and fixtures for various testing frameworks.

## When to Use

- "Create a mock for this function"
- "Generate test fixtures"
- "Mock this API response"
- "Create stubs for testing"
- "Generate mock data"
- "Mock this class/module"

## Instructions

### 1. Identify What to Mock

Ask the user or analyze code to determine:
- What needs to be mocked (function, class, API, database, etc.)
- Which testing framework is used
- What the mock behavior should be
- What data the mock should return

Scan for testing framework:

```bash
# Check package.json for testing framework
grep -E "(jest|vitest|mocha|jasmine|pytest|unittest|minitest)" package.json

# Check for test files
find . -name "*.test.*" -o -name "*.spec.*" -o -name "test_*.py"
```

### 2. Determine Mock Type

**Function Mocks:**
- Simple return value
- Multiple return values
- Implementations
- Spy on function calls

**API Mocks:**
- HTTP request/response
- WebSocket messages
- GraphQL queries
- REST endpoints

**Class Mocks:**
- Instance methods
- Static methods
- Properties
- Constructors

**Module Mocks:**
- Entire module
- Partial module
- Default exports
- Named exports

### 3. Generate Mocks by Framework

## JavaScript/TypeScript Mocks

### Jest Mocks

**Simple Function Mock:**
```javascript
// Mock a simple function
const mockFn = jest.fn()
mockFn.mockReturnValue(42)

// Use in test
test('uses mocked function', () => {
  expect(mockFn()).toBe(42)
  expect(mockFn).toHaveBeenCalled()
})
```

**Function with Different Return Values:**
```javascript
const mockFn = jest.fn()
  .mockReturnValueOnce('first')
  .mockReturnValueOnce('second')
  .mockReturnValue('default')

expect(mockFn()).toBe('first')
expect(mockFn()).toBe('second')
expect(mockFn()).toBe('default')
```

**Mock Implementation:**
```javascript
const mockFn = jest.fn((x, y) => x + y)

expect(mockFn(1, 2)).toBe(3)
expect(mockFn).toHaveBeenCalledWith(1, 2)
```

**Module Mock:**
```javascript
// __mocks__/axios.js
export default {
  get: jest.fn(() => Promise.resolve({ data: {} })),
  post: jest.fn(() => Promise.resolve({ data: {} })),
}

// In test file
jest.mock('axios')
import axios from 'axios'

test('fetches data', async () => {
  axios.get.mockResolvedValue({ data: { name: 'John' } })

  const result = await fetchUser(1)

  expect(result.name).toBe('John')
  expect(axios.get).toHaveBeenCalledWith('/users/1')
})
```

**Class Mock:**
```javascript
// Mock a class
jest.mock('./Database')
import Database from './Database'

Database.mockImplementation(() => ({
  query: jest.fn().mockResolvedValue([{ id: 1, name: 'John' }]),
  connect: jest.fn().mockResolvedValue(true),
  disconnect: jest.fn().mockResolvedValue(true),
}))

test('uses database', async () => {
  const db = new Database()
  const users = await db.query('SELECT * FROM users')

  expect(users).toHaveLength(1)
  expect(db.query).toHaveBeenCalled()
})
```

**Partial Mock:**
```javascript
// Mock only specific methods
import * as utils from './utils'

jest.spyOn(utils, 'fetchData').mockResolvedValue({ data: 'mocked' })

test('uses mocked method', async () => {
  const result = await utils.fetchData()
  expect(result.data).toBe('mocked')
})
```

### Vitest Mocks

**Function Mock:**
```javascript
import { vi, expect, test } from 'vitest'

const mockFn = vi.fn()
mockFn.mockReturnValue(42)

test('uses mock', () => {
  expect(mockFn()).toBe(42)
})
```

**Module Mock:**
```javascript
// __mocks__/api.ts
import { vi } from 'vitest'

export const fetchUser = vi.fn()
export const createUser = vi.fn()

// In test
vi.mock('./api')
import { fetchUser } from './api'

test('fetches user', async () => {
  fetchUser.mockResolvedValue({ id: 1, name: 'John' })

  const user = await fetchUser(1)

  expect(user.name).toBe('John')
})
```

**Spy on Method:**
```javascript
import { vi } from 'vitest'

const obj = {
  method: () => 'original'
}

vi.spyOn(obj, 'method').mockReturnValue('mocked')

expect(obj.method()).toBe('mocked')
```

### TypeScript Mocks

**Type-Safe Mock:**
```typescript
import { vi } from 'vitest'

interface User {
  id: number
  name: string
  email: string
}

// Create type-safe mock
const mockUser: User = {
  id: 1,
  name: 'John Doe',
  email: '[email protected]'
}

// Mock function with types
const mockFetchUser = vi.fn<[id: number], Promise<User>>()
mockFetchUser.mockResolvedValue(mockUser)
```

**Mock Factory:**
```typescript
// Create a factory for generating mocks
function createMockUser(overrides?: Partial<User>): User {
  return {
    id: 1,
    name: 'Test User',
    email: '[email protected]',
    ...overrides
  }
}

// Use in tests
const user1 = createMockUser({ name: 'Alice' })
const user2 = createMockUser({ id: 2, email: '[email protected]' })
```

## Python Mocks

### unittest.mock

**Function Mock:**
```python
from unittest.mock import Mock

# Simple mock
mock_func = Mock(return_value=42)
assert mock_func() == 42
assert mock_func.called

# Mock with side effects
mock_func = Mock(side_effect=[1, 2, 3])
assert mock_func() == 1
assert mock_func() == 2
assert mock_func() == 3
```

**Patch Decorator:**
```python
from unittest.mock import patch, Mock

@patch('requests.get')
def test_fetch_data(mock_get):
    # Setup mock
    mock_response = Mock()
    mock_response.json.return_value = {'name': 'John'}
    mock_response.status_code = 200
    mock_get.return_value = mock_response

    # Test
    result = fetch_user_data(1)

    assert result['name'] == 'John'
    mock_get.assert_called_once_with('https://api.example.com/users/1')
```

**Class Mock:**
```python
from unittest.mock import Mock, patch

@patch('database.Database')
def test_database_query(mock_database_class):
    # Setup mock instance
    mock_db = Mock()
    mock_db.query.return_value = [{'id': 1, 'name': 'John'}]
    mock_database_class.return_value = mock_db

    # Test
    db = Database()
    users = db.query('SELECT * FROM users')

    assert len(users) == 1
    assert users[0]['name'] == 'John'
    mock_db.query.assert_called_once()
```

**Context Manager Mock:**
```python
from unittest.mock import patch, mock_open

# Mock file operations
mock_data = "file contents"
with patch('builtins.open', mock_open(read_data=mock_data)):
    with open('file.txt') as f:
        content = f.read()
    assert content == mock_data
```

### pytest Fixtures

**Simple Fixture:**
```python
import pytest

@pytest.fixture
def mock_user():
    return {
        'id': 1,
        'name': 'John Doe',
        'email': '[email protected]'
    }

def test_user_data(mock_user):
    assert mock_user['name'] == 'John Doe'
```

**Fixture with Cleanup:**
```python
@pytest.fixture
def mock_database():
    # Setup
    db = MockDatabase()
    db.connect()

    yield db  # Provide to test

    # Teardown
    db.disconnect()

def test_database_query(mock_database):
    result = mock_database.query('SELECT * FROM users')
    assert len(result) > 0
```

**Parametrized Fixture:**
```python
@pytest.fixture(params=[
    {'name': 'Alice', 'age': 25},
    {'name': 'Bob', 'age': 30},
    {'name': 'Charlie', 'age': 35}
])
def mock_user(request):
    return request.param

def test_user_age(mock_user):
    assert mock_user['age'] > 0
```

### pytest-mock

```python
def test_api_call(mocker):
    # Mock a function
    mock_get = mocker.patch('requests.get')
    mock_get.return_value.json.return_value = {'status': 'ok'}

    result = fetch_data()

    assert result['status'] == 'ok'
    mock_get.assert_called_once()
```

## API Response Mocks

### REST API Mock

```javascript
// Mock fetch API
global.fetch = jest.fn(() =>
  Promise.resolve({
    ok: true,
    status: 200,
    json: async () => ({
      id: 1,
      name: 'John Doe',
      email: '[email protected]'
    }),
    headers: new Headers({
      'Content-Type': 'application/json'
    })
  })
)

test('fetches user', async () => {
  const user = await fetchUser(1)

  expect(user.name).toBe('John Doe')
  expect(fetch).toHaveBeenCalledWith('/api