testing

What this skill does

# Testing

This skill provides comprehensive testing capabilities including test strategy, automation setup, Test-Driven Development (TDD), test writing best practices, coverage analysis, CI/CD integration, and web application testing with Playwright.

## When to Use This Skill

- When setting up test infrastructure for a project
- When creating test strategies and test plans
- When writing unit, integration, or E2E tests
- When implementing TDD/test-first development
- When analyzing test coverage and quality
- When integrating tests into CI/CD pipelines
- When testing web applications with Playwright
- When debugging test failures or improving test reliability
- When writing test fixtures, mock data, or factory functions
- When mocking external dependencies (APIs, databases, file systems)
- When organizing test file structure and test suites
- When testing async code, Promises, or event-driven behavior
- When implementing snapshot tests for UI components
- When configuring test coverage thresholds

## What This Skill Does

1. **Test Strategy**: Designs comprehensive testing strategies (unit, integration, E2E)
2. **Test Automation**: Sets up test frameworks and automation tools
3. **TDD Methodology**: Implements Test-Driven Development workflows (Red-Green-Refactor)
4. **Test Writing**: Writes focused, maintainable tests with proper patterns
5. **Coverage Analysis**: Analyzes and improves test coverage
6. **CI/CD Integration**: Integrates tests into continuous integration pipelines
7. **Web App Testing**: Tests web applications using Playwright
8. **Test Quality**: Improves test reliability and maintainability

## Test Strategy

### Test Pyramid

**Recommended Distribution:**

- **Unit Tests**: 70% - Fast, isolated, test individual functions
- **Integration Tests**: 20% - Test component interactions
- **E2E Tests**: 10% - Test complete user workflows

**Test Types:**

- Functional tests (happy path, edge cases, error handling)
- Non-functional tests (performance, security, accessibility)
- Regression tests (prevent breaking changes)
- Smoke tests (critical path verification)

### Framework Selection

**JavaScript/TypeScript:**

- Jest, Vitest, Mocha for unit/integration
- Playwright, Cypress for E2E
- React Testing Library for component testing

**Python:**

- pytest for unit/integration
- Selenium, Playwright for E2E
- unittest for standard library testing

**Java:**

- JUnit for unit tests
- TestNG for integration
- Selenium for E2E

**Go:**

- Built-in testing package
- Testify for assertions

**Rust:**

- Built-in test framework
- Cargo test for running tests

## Test-Driven Development (TDD)

TDD is a **design technique**, not just a testing technique. It produces better-designed, more maintainable code through small, disciplined steps.

### Core Principle

**Write tests before code. Always.** TDD forces you to think about:

- What behavior do I need?
- How will I know it works?
- What's the simplest implementation?

### The Three Laws (Never Violate)

1. **Write NO production code** without a failing test first
2. **Write only enough test** to demonstrate one failure
3. **Write only enough code** to pass that test

### Red-Green-Refactor Cycle

**Phase 1: RED - Write Failing Test**

1. Write ONE test that defines desired behavior
2. Run test - verify it FAILS
3. Verify it fails for the RIGHT reason (not syntax error)
4. DO NOT write implementation yet

**Phase 2: GREEN - Minimal Implementation**

1. Write MINIMAL code to make test pass
2. Resist urge to add extra features
3. Run test - verify it PASSES
4. If test still fails, fix implementation (not test)

**Phase 3: REFACTOR - Clean Code**

1. Remove code duplication (DRY)
2. Improve naming for clarity
3. Extract complex logic into functions
4. Run ALL tests - must stay green throughout
5. Check test coverage on changed lines

After REFACTOR, start new RED phase for next behavior.

## Test Writing Patterns

### Arrange-Act-Assert (AAA)

**Structure:**

1. **Arrange**: Set up test data and conditions
2. **Act**: Execute the code being tested
3. **Assert**: Verify the expected outcome

**Example:**

```javascript
describe('UserService', () => {
  it('should create user with valid data', async () => {
    // Arrange
    const userData = { email: '[email protected]', name: 'Test User' };

    // Act
    const result = await userService.createUser(userData);

    // Assert
    expect(result).toHaveProperty('id');
    expect(result.email).toBe(userData.email);
  });
});
```

### Given-When-Then (BDD Style)

**Structure:**

1. **Given**: Initial context/preconditions
2. **When**: Action/event that triggers behavior
3. **Then**: Expected outcome

### Test Organization

**File Structure:**

```
project/
├── src/
│   └── components/
│       └── User.jsx
├── tests/
│   ├── unit/
│   │   └── User.test.jsx
│   ├── integration/
│   │   └── UserAPI.test.js
│   └── e2e/
│       └── user-flow.spec.js
├── jest.config.js
└── playwright.config.js
```

## Coverage Analysis

### Coverage Goals

**Recommended Thresholds:**

- **Lines**: 80%+
- **Functions**: 80%+
- **Branches**: 80%+
- **Statements**: 80%+

**Critical Paths:**

- Always aim for 100% coverage on critical business logic
- Authentication and authorization
- Payment processing
- Data validation

### Coverage Gaps

**Common Gaps:**

- Error handling paths
- Edge cases
- Boundary conditions
- Integration points

**Improvement Strategies:**

- Identify untested code paths
- Add tests for error scenarios
- Test edge cases and boundaries
- Increase integration test coverage

## CI/CD Integration

### Test Pipeline

**Stages:**

1. **Unit Tests**: Fast feedback, run on every commit
2. **Integration Tests**: Run on pull requests
3. **E2E Tests**: Run before merging to main
4. **Performance Tests**: Run on main branch

**Quality Gates:**

- All tests must pass
- Coverage must meet threshold
- No critical security issues
- Performance benchmarks met

## Web Application Testing with Playwright

### Helper Scripts

This skill includes Python helper scripts in `scripts/`:

- **`with_server.py`** - Manages server lifecycle (supports multiple servers). Always run with `--help` first to see usage.

  ```bash
  # Single server
  python scripts/with_server.py --server "npm run dev" --port 5173 -- python your_automation.py

  # Multiple servers (e.g., backend + frontend)
  python scripts/with_server.py \
    --server "cd backend && python server.py" --port 3000 \
    --server "cd frontend && npm run dev" --port 5173 \
    -- python your_automation.py
  ```

### Decision Tree: Choosing Your Approach

```
User task → Is it static HTML?
    ├─ Yes → Read HTML file directly to identify selectors
    │         ├─ Success → Write Playwright script using selectors
    │         └─ Fails/Incomplete → Treat as dynamic (below)
    │
    └─ No (dynamic webapp) → Is the server already running?
        ├─ No → Run: python scripts/with_server.py --help
        │        Then use the helper + write simplified Playwright script
        │
        └─ Yes → Reconnaissance-then-action:
            1. Navigate and wait for networkidle
            2. Take screenshot or inspect DOM
            3. Identify selectors from rendered state
            4. Execute actions with discovered selectors
```

### Playwright Best Practices

- **Use bundled scripts as black boxes** - Use `--help` to see usage, then invoke directly
- Use `sync_playwright()` for synchronous scripts
- Always close the browser when done
- Use descriptive selectors: `text=`, `role=`, CSS selectors, or IDs
- Add appropriate waits: `page.wait_for_selector()` or `page.wait_for_timeout()`
- **CRITICAL**: Wait for `page.wait_for_load_state('networkidle')` before inspection on dynamic apps

### Example: Basic Playwright Script

```python
from playwright.sync_api import sync_playwright

with sync_playwright() as p:
    browser = p.chromium.launch(headless=True)
    page = browser.new_page()
    page.goto('http://localhost:5173')
    pa