
using Xunit;
namespace ConsoleApp {
    public class ProgramTests {
        [Fact(DisplayName = "CalculateFactorial returns correct factorial for positive integers")] 
        public void CalculateFactorial_PositiveIntegers_ReturnsCorrectFactorial() {
            Assert.Equal(120, Program.CalculateFactorial(5));
            Assert.Equal(24, Program.CalculateFactorial(4));
            Assert.Equal(6, Program.CalculateFactorial(3));
        }

        [Fact(DisplayName = "CalculateFactorial returns 1 for input 0")]
        public void CalculateFactorial_Zero_ReturnsOne() {
            Assert.Equal(1, Program.CalculateFactorial(0));
        }

        [Fact(DisplayName = "CalculateFactorial returns 1 for input 1")]
        public void CalculateFactorial_One_ReturnsOne() {
            Assert.Equal(1, Program.CalculateFactorial(1));
        }

        [Fact(DisplayName = "CalculateFactorial throws ArgumentException for negative input")]
        public void CalculateFactorial_NegativeInput_ThrowsArgumentException() {
            var ex = Assert.Throws<ArgumentException>(() => Program.CalculateFactorial(-3));
            Assert.Equal("Input must be non-negative.", ex.Message);
        }
    }
}

ProgramTests.cs

Master the art of writing modular, reusable, and clear code in C# by learning how to create, use, and reason about methods. This course guides you from the basics of function signatures to advanced modularization techniques, with engaging real-world challenges and step-by-step explanations.

Explore the fundamentals of C# methods, including defining, calling, and understanding different parameter and return types. Practice writing and using methods with a variety of signatures.

Learn how to write methods that return arrays, and how to refactor repetitive loops into reusable functions for cleaner code.

Explore the concepts of pure and impure functions, and learn how to break down complex problems into smaller, manageable methods using stepwise decomposition.

Challenge: Pure Function Practice

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