testing

Testing Best Practices

This skill provides testing patterns, frameworks, and best practices applicable across multiple programming languages and frameworks.

When to Use

✅ DO Write Tests For:

• Business logic and domain rules
• API endpoints and routes
• Service methods and utilities
• Error handling and edge cases
• Integration points (external services, databases)
• Critical user flows

❌ DON'T Write Tests For:

• Simple getters/setters
• Framework code (unless custom)
• Third-party library code
• Trivial code with no logic
• Generated code

Core Concepts

Test Types

Unit Tests:

• Test individual functions/methods in isolation
• Fast execution (< 1ms per test)
• No external dependencies (mocked)
• High code coverage

Integration Tests:

• Test multiple components working together
• May include database, file system, or external services
• Slower execution
• Verify contracts and interfaces

End-to-End (E2E) Tests:

• Test complete user workflows
• Full system stack
• Slowest execution
• Verify system behavior from user perspective

Test Structure (AAA Pattern)

Arrange: Set up test data and conditions Act: Execute the code under test Assert: Verify the expected outcome

// Example: TypeScript/Jest
describe('OrderService', () => {
  it('should calculate total with tax', () => {
    // Arrange
    const order = { items: [{ price: 100 }], taxRate: 0.1 };
    
    // Act
    const total = calculateTotal(order);
    
    // Assert
    expect(total).toBe(110);
  });
});

// Example: C#/xUnit
public class OrderServiceTests
{
    [Fact]
    public void CalculateTotal_WithTax_ReturnsCorrectTotal()
    {
        // Arrange
        var order = new Order { Items = new[] { new Item { Price = 100 } }, TaxRate = 0.1m };
        
        // Act
        var total = _service.CalculateTotal(order);
        
        // Assert
        Assert.Equal(110m, total);
    }
}

Testing Patterns

Pattern 1: Unit Test Structure