# ADR-002: Testing Pyramid Strategy

## Status
**ACCEPTED** - 2024-09-08

## Context
To maintain the highest quality standards and achieve near-100% test coverage, we need a comprehensive testing strategy that covers all aspects of our applications from unit tests to end-to-end testing.

## Decision
We implement a **full testing pyramid** with multiple layers of testing to ensure comprehensive coverage and quality assurance.

### Testing Pyramid Structure

#### 1. Unit Tests (70% of tests)
- **Purpose**: Test individual functions, methods, and components in isolation
- **Scope**: Fast, focused tests for specific functionality
- **Tools**: Rust built-in testing, `cargo test`
- **Coverage**: Every public function and method

#### 2. Integration Tests (20% of tests)
- **Purpose**: Test interactions between components and modules
- **Scope**: Test component integration and data flow
- **Tools**: Rust integration tests, `wasm-bindgen-test`
- **Coverage**: API endpoints, database interactions, external service integration

#### 3. End-to-End Tests (10% of tests)
- **Purpose**: Test complete user workflows and application behavior
- **Scope**: Full application testing from user perspective
- **Tools**: Playwright, browser automation
- **Coverage**: Critical user journeys and business workflows

### Testing Standards

#### Coverage Requirements
- **Minimum coverage**: 95% line coverage
- **Branch coverage**: 90% branch coverage
- **Function coverage**: 100% public function coverage
- **Integration coverage**: 100% API endpoint coverage

#### Test Quality Standards
- **Fast execution**: Unit tests must run in <1ms each
- **Isolated**: Tests must not depend on external state
- **Deterministic**: Tests must produce consistent results
- **Readable**: Tests must clearly express intent and expected behavior

## Implementation

### Unit Testing Strategy
```rust
// Example: Data processing unit tests
#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_data_validation() {
        let validator = DataValidator::new();
        assert!(validator.validate("valid_data"));
        assert!(!validator.validate("invalid_data"));
    }

    #[test]
    fn test_data_transformation() {
        let transformer = DataTransformer::new();
        let input = vec![1, 2, 3];
        let expected = vec![2, 4, 6];
        assert_eq!(transformer.double(input), expected);
    }
}
```

### Integration Testing Strategy
```rust
// Example: API integration tests
#[cfg(test)]
mod integration_tests {
    use super::*;

    #[tokio::test]
    async fn test_api_endpoint() {
        let app = create_test_app().await;
        let response = app.post("/api/data")
            .json(&test_data())
            .send()
            .await
            .unwrap();
        
        assert_eq!(response.status(), 200);
        let result: ApiResponse = response.json().await.unwrap();
        assert!(result.success);
    }
}
```

### End-to-End Testing Strategy
```typescript
// Example: Playwright E2E tests
test.describe('Data Pipeline Workflow', () => {
  test('should complete full data processing workflow', async ({ page }) => {
    // Navigate to application
    await page.goto('/');
    
    // Upload data
    await page.setInputFiles('[data-testid="file-upload"]', 'test-data.csv');
    
    // Configure pipeline
    await page.selectOption('[data-testid="processor-type"]', 'rust-processor');
    await page.fill('[data-testid="output-format"]', 'json');
    
    // Execute pipeline
    await page.click('[data-testid="start-processing"]');
    
    // Verify results
    await expect(page.locator('[data-testid="processing-status"]'))
      .toContainText('Complete');
    await expect(page.locator('[data-testid="download-link"]'))
      .toBeVisible();
  });
});
```

### Test Organization
```
tests/
├── unit/                    # Unit tests
│   ├── data_processing.rs
│   ├── validation.rs
│   └── transformation.rs
├── integration/             # Integration tests
│   ├── api_tests.rs
│   ├── database_tests.rs
│   └── service_tests.rs
└── e2e/                     # End-to-end tests
    ├── user_workflows.spec.ts
    ├── data_pipeline.spec.ts
    └── performance.spec.ts
```

## Quality Gates

### Pre-commit Hooks
- Run unit tests
- Check code coverage
- Lint and format code
- Security vulnerability scan

### CI/CD Pipeline
1. **Unit tests**: Run on every commit
2. **Integration tests**: Run on pull requests
3. **E2E tests**: Run on main branch
4. **Coverage report**: Generate and enforce coverage thresholds
5. **Performance tests**: Run benchmarks and regression tests

### Coverage Monitoring
- **Real-time coverage**: Track coverage during development
- **Coverage reports**: Generate detailed coverage reports
- **Coverage trends**: Monitor coverage trends over time
- **Coverage alerts**: Alert when coverage drops below thresholds

## Tools and Technologies

### Rust Testing
- **cargo test**: Built-in testing framework
- **criterion**: Benchmarking and performance testing
- **tarpaulin**: Code coverage analysis
- **mockall**: Mocking framework for unit tests

### Web Testing
- **Playwright**: End-to-end testing
- **wasm-bindgen-test**: WebAssembly testing
- **js-sys**: JavaScript interop testing
- **web-sys**: Web API testing

### CI/CD Integration
- **GitHub Actions**: Automated testing pipeline
- **Coverage reporting**: Integration with coverage services
- **Test result reporting**: Detailed test result analysis
- **Performance monitoring**: Continuous performance testing

## Metrics and Monitoring

### Test Metrics
- **Test execution time**: Track test suite performance
- **Test coverage**: Monitor coverage percentages
- **Test reliability**: Track flaky test identification
- **Test maintenance**: Monitor test maintenance overhead

### Quality Metrics
- **Bug escape rate**: Measure bugs found in production
- **Mean time to detection**: Track time to find issues
- **Mean time to resolution**: Track time to fix issues
- **Customer satisfaction**: Monitor client feedback on quality

## Review and Updates
This ADR will be reviewed monthly to ensure testing strategy remains effective and aligned with project needs. Updates will be made based on:
- Team feedback and experience
- Industry best practices
- Tool and technology updates
- Client requirements and feedback

## Related ADRs
- ADR-001: Test-Driven Development (TDD) First Approach
- ADR-003: Playwright Testing for Demos
- ADR-004: Code Coverage Standards
- ADR-005: Performance Testing Strategy
