
using Xunit;
namespace ConsoleApp {
    public class ProgramTests {
        [Fact(DisplayName = "Calculate returns correct sum for 'add'")]
        public void Calculate_ReturnsSum_WhenAdd()
        {
            Assert.Equal(15, Program.Calculate(10, 5, "add"));
        }

        [Fact(DisplayName = "Calculate returns correct difference for 'subtract'")]
        public void Calculate_ReturnsDifference_WhenSubtract()
        {
            Assert.Equal(5, Program.Calculate(10, 5, "subtract"));
        }

        [Fact(DisplayName = "Calculate returns correct product for 'multiply'")]
        public void Calculate_ReturnsProduct_WhenMultiply()
        {
            Assert.Equal(50, Program.Calculate(10, 5, "multiply"));
        }

        [Fact(DisplayName = "Calculate returns correct integer division for 'divide'")]
        public void Calculate_ReturnsQuotient_WhenDivide()
        {
            Assert.Equal(2, Program.Calculate(10, 5, "divide"));
        }

        [Fact(DisplayName = "Calculate throws ArgumentException with correct message when dividing by zero")]
        public void Calculate_ThrowsArgumentException_WhenDivideByZero()
        {
            var ex = Assert.Throws<ArgumentException>(() => Program.Calculate(10, 0, "divide"));
            Assert.Equal("Cannot divide by zero.", ex.Message);
        }

        [Fact(DisplayName = "Calculate throws ArgumentException with correct message for invalid operation")]
        public void Calculate_ThrowsArgumentException_WhenInvalidOperation()
        {
            var ex = Assert.Throws<ArgumentException>(() => Program.Calculate(10, 5, "modulo"));
            Assert.Equal("Invalid operation.", 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: Simple Calculator

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