Testing Tdd

Testing & TDD Workflow

Apply Test-Driven Development methodology to ensure reliability and confidence when adding new features.

TDD Workflow

Follow this cycle for all new features:

1. Write the Test First

Frontend (JavaScript/TypeScript)

• Use Vitest for all frontend tests
• Name tests clearly and descriptively

Backend (C#/.NET)

• Use xUnit or MsTest (based on project)
• Follow the same naming conventions

Test Naming Convention

shouldDoSomethingWhenCondition()

2. Generate Code

• Write the minimal code needed to make the test pass
• Use GitHub Copilot to help implement based on the test
• Keep implementations simple and focused

3. Run Tests and Iterate

• Run the test suite
• Fix failures
• Refactor if needed
• Repeat until all tests pass

Testing Best Practices

Coverage

• Write tests for all new features and bug fixes
• Ensure tests cover edge cases and error handling
• Test both happy paths and error scenarios

Test Quality

• Keep tests focused and isolated
• One assertion concept per test
• Use descriptive test names that explain the scenario
• NEVER change the original code to make it easier to test

Test Structure (AAA Pattern)

// Arrange - Set up test data and conditions
// Act - Execute the code being tested
// Assert - Verify the results

Examples

Frontend Test (Vitest)

import { describe, it, expect } from 'vitest'
import { calculateTotal } from './cart'

describe('calculateTotal', () => {
	it('shouldReturnZeroWhenCartIsEmpty', () => {
		// Arrange
		const cart = []

		// Act
		const total = calculateTotal(cart)

		// Assert
		expect(total).toBe(0)
	})

	it('shouldCalculateTotalWithMultipleItems', () => {
		// Arrange
		const cart = [
			{ price: 10, quantity: 2 },
			{ price: 5, quantity: 3 }
		]

		// Act
		const total = calculateTotal(cart)

		// Assert
		expect(total).toBe(35)
	})

	it('shouldThrowErrorWhenItemHasNegativePrice', () => {
		// Arrange
		const cart = [{ price: -10, quantity: 1 }]

		// Act & Assert
		expect(() => calculateTotal(cart)).toThrow('Price cannot be negative')
	})
})

Backend Test (xUnit)

using Xunit;

public class CartCalculatorTests
{
    [Fact]
    public void ShouldReturnZeroWhenCartIsEmpty()
    {
        // Arrange
        var cart = new List<CartItem>();
        var calculator = new CartCalculator();

        // Act
        var total = calculator.CalculateTotal(cart);

        // Assert
        Assert.Equal(0, total);
    }

    [Fact]
    public void ShouldCalculateTotalWithMultipleItems()
    {
        // Arrange
        var cart = new List<CartItem>
        {
            new CartItem { Price = 10, Quantity = 2 },
            new CartItem { Price = 5, Quantity = 3 }
        };
        var calculator = new CartCalculator();

        // Act
        var total = calculator.CalculateTotal(cart);

        // Assert
        Assert.Equal(35, total);
    }

    [Fact]
    public void ShouldThrowExceptionWhenItemHasNegativePrice()
    {
        // Arrange
        var cart = new List<CartItem> { new CartItem { Price = -10, Quantity = 1 } };
        var calculator = new CartCalculator();

        // Act & Assert
        Assert.Throws<ArgumentException>(() => calculator.CalculateTotal(cart));
    }
}

TDD Benefits

Following this workflow ensures:

• ✅ Code is testable by design
• ✅ Better code coverage
• ✅ Fewer bugs in production
• ✅ Confidence when refactoring
• ✅ Living documentation through tests
• ✅ Faster development in the long run

When to Apply

Apply TDD when:

• Implementing new features
• Fixing bugs (write a failing test first)
• Refactoring existing code
• User requests testing implementation
• Starting a new project or module