Continue Developing the calculateDiscount Function

Welcome to your second lesson, which continues to delve into Test Driven Development (TDD) practices using a new C# and xUnit. In this unit, we will extend the functionality of our CalculateDiscount function by implementing five new requirements.

Building on the previous unit, this course emphasizes practical experience by sequentially providing requirements through tests. Your mission is to implement code that satisfies each test, mirroring a real-world TDD scenario. Consider this guide your pair programmer, offering test-driven prompts to enhance your expertise incrementally.

As a reminder, the Red-Green-Refactor cycle is crucial in TDD, steering your development process:

• Red: Begin by writing a failing test to define what to do next.
• Green: Develop just enough code to pass the test, concentrating on meeting the functionality.
• Refactor: Enhance the code for clarity and efficiency without changing its behavior.

• Description: The function should not accept negative discount percentages and must throw an error in such cases.
• Test Case:
    [Fact]
    public void Should_Throw_Exception_For_Discounts_Less_Than_ZeroPercent()
    {
        // Arrange
        decimal originalPrice = 100;
        decimal discountPercentage = -10;
  
        // Act & Assert
        var exception = Assert.Throws<ArgumentException>(() => CalculateDiscount(originalPrice, discountPercentage));
        Assert.Equal("Discount cannot be negative", exception.Message);
    }

• Description: The function should ensure that discounted prices don’t dip below the minimum limit due to very small original prices.
• Test Case:
    [Fact]
    public void CalculateDiscount_HandlesVerySmallPricesCorrectly()
    {
        // Arrange
        var math = new Math();
        var originalPrice = 0.001;
        var discountPercentage = 1;
        var expectedDiscountedPrice = 0.01; // Should not go below 0.01
  
        // Act
        var result = math.CalculateDiscount(originalPrice, discountPercentage);
  
        // Assert
        Assert.Equal(expectedDiscountedPrice, result);
    }