
using Xunit;
namespace ConsoleApp {
    public class ProgramTests {
        [Fact(DisplayName = "Throws ArgumentException with correct message if username is null")]
        public void RegisterUser_ThrowsIfUsernameNull() {
            var ex = Assert.Throws<ArgumentException>(() => Program.RegisterUser(null, "password"));
            Assert.Equal("Username cannot be null or empty.", ex.Message);
        }

        [Fact(DisplayName = "Throws ArgumentException with correct message if username is empty")]
        public void RegisterUser_ThrowsIfUsernameEmpty() {
            var ex = Assert.Throws<ArgumentException>(() => Program.RegisterUser("", "password"));
            Assert.Equal("Username cannot be null or empty.", ex.Message);
        }

        [Fact(DisplayName = "Throws ArgumentException with correct message if password is null")]
        public void RegisterUser_ThrowsIfPasswordNull() {
            var ex = Assert.Throws<ArgumentException>(() => Program.RegisterUser("bob", null));
            Assert.Equal("Password cannot be null or empty.", ex.Message);
        }

        [Fact(DisplayName = "Throws ArgumentException with correct message if password is empty")]
        public void RegisterUser_ThrowsIfPasswordEmpty() {
            var ex = Assert.Throws<ArgumentException>(() => Program.RegisterUser("bob", ""));
            Assert.Equal("Password cannot be null or empty.", ex.Message);
        }

        [Fact(DisplayName = "Returns correct success message if both username and password are valid")]
        public void RegisterUser_ReturnsSuccessMessage() {
            string result = Program.RegisterUser("alice", "password123");
            Assert.Equal("User 'alice' registered successfully.", result);
        }
    }
}

ProgramTests.cs

Master the art of robust C# programming by learning how to handle, create, and debug exceptions. This hands-on course guides you through real-world error handling scenarios, from basic try-catch to custom exceptions and safe file operations.

Learn the basics of exceptions in C#, how to use try-catch blocks, and why error handling is crucial for robust applications.

Learn to create your own exception types and use guard clauses to prevent invalid states in your code.

Master techniques for validating user input and safely parsing data to prevent runtime errors.

Handle file operations safely and learn to debug exceptions using stack traces and refactoring techniques.

Challenge: Guard Clauses in User Registration

Solution

Challenge: Guard Clauses in User Registration

Solution