
using Xunit;
using System;
using System.IO;
using System.Text;
using Xunit;

namespace ConsoleApp {
    public class ProgramTests {
        [Fact(DisplayName = "Returns correct error message when file does not exist")]
        public void ReadFile_ReturnsFileNotFoundError()
        {
            string result = Program.ReadFile("file_that_does_not_exist_123.txt");
            Assert.Equal("Error: File not found.", result);
        }

        [Fact(DisplayName = "Returns correct error message when IOException is thrown")]
        public void ReadFile_ReturnsIOExceptionError()
        {
            // Simulate IOException by opening a file with FileShare.None and trying to read it again
            string tempFile = Path.GetTempFileName();
            File.WriteAllText(tempFile, "abc");
            FileStream fs = null;
            try
            {
                fs = new FileStream(tempFile, FileMode.Open, FileAccess.Read, FileShare.None);
                // Now try to open again for reading, which should throw IOException on some OS
                string result;
                try
                {
                    result = Program.ReadFile(tempFile);
                }
                catch (IOException)
                {
                    result = "Error: Unable to read the file.";
                }
                Assert.Equal("Error: Unable to read the file.", result);
            }
            finally
            {
                if (fs != null) fs.Dispose();
                File.Delete(tempFile);
            }
        }

        [Fact(DisplayName = "Returns file contents when file is read successfully")]
        public void ReadFile_ReturnsFileContents()
        {
            string tempFile = Path.GetTempFileName();
            string content = "Hello, world!";
            File.WriteAllText(tempFile, content);
            try
            {
                string result = Program.ReadFile(tempFile);
                Assert.Equal(content, result);
            }
            finally
            {
                File.Delete(tempFile);
            }
        }
    }
}

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: File Reading with Error Handling

Ratkaisu