using NUnit.Framework;

using System;

using System.IO;

​

public class CaseConverter

{

    /// <summary>

    /// Convert a string into different case as per user's choice

    /// </summary>

    /// <param></param>

    /// <returns></returns>

    public static void CaseConversion()

    {

        Console.WriteLine("Enter a string:");

        string inputString = Console.ReadLine();

​

        if (string.IsNullOrEmpty(inputString))

        {

            Console.WriteLine("Input string cannot be null or empty.");

            return;

        }

​

        Console.WriteLine("Choose a case conversion option:");

        Console.WriteLine("1. To Upper Case");

        Console.WriteLine("2. To Lower Case");

        Console.WriteLine("3. To Toggle Case");

​

        Console.WriteLine("Enter your choice (1, 2, or 3):");

        string choice = Console.ReadLine();

​

        switch (choice)

        {

            case "1":

                Console.WriteLine("Upper Case: " + inputString.ToUpper());

                break;

            case "2":

                Console.WriteLine("Lower Case: " + inputString.ToLower());

                break;

            case "3":

                Console.WriteLine("Toggle Case: " + ToggleCase(inputString));

                break;

            default:

                Console.WriteLine("Invalid choice.");

                break;

        }

    }

​

    private static string ToggleCase(string input)

    {

        char[] chars = input.ToCharArray();

        for (int i = 0; i < chars.Length; i++)

        {

            if (char.IsUpper(chars[i]))

            {

                chars[i] = char.ToLower(chars[i]);

            }

            else if (char.IsLower(chars[i]))

            {

                chars[i] = char.ToUpper(chars[i]);

            }

        }

        return new string(chars);

    }

}

​

[TestFixture]

public class CaseConverterTests

{

    [Test]

    public void CaseConversion_NullOrEmptyInput_PrintsErrorMessage()

    {

        // Arrange

        using (var consoleOutput = new StringWriter())

        {

            Console.SetOut(consoleOutput);

​

            // Act

            // Simulate user input (empty string in this case)

            string input = string.Empty;

            var stringReader = new StringReader(input + Environment.NewLine + "1"); // Provide "1" to avoid further input requests

            Console.SetIn(stringReader);

​

            CaseConverter.CaseConversion();

​

            // Assert

            Assert.That(consoleOutput.ToString().Contains("Input string cannot be null or empty."), Is.True);

        }

    }

​

    [Test]

    public void CaseConversion_InvalidChoice_PrintsErrorMessage()

    {

        // Arrange

        using (var consoleOutput = new StringWriter())

        {

            Console.SetOut(consoleOutput);

​

            // Act

            // Simulate user input (invalid choice)

            string input = "test";

            var stringReader = new StringReader(input + Environment.NewLine + "4");

            Console.SetIn(stringReader);

​

            CaseConverter.CaseConversion();

​

            // Assert

            Assert.That(consoleOutput.ToString().Contains("Invalid choice."), Is.True);

        }

    }

​

    [Test]

    public void CaseConversion_ToUpper_PrintsUpperCaseString()

    {

        // Arrange

        using (var consoleOutput = new StringWriter())

        {

            Console.SetOut(consoleOutput);

​

            // Act

            // Simulate user input (string and choice 1)

            string input = "test";

            var stringReader = new StringReader(input + Environment.NewLine + "1");

            Console.SetIn(stringReader);

​

            CaseConverter.CaseConversion();

​

            // Assert

            Assert.That(consoleOutput.ToString().Contains("Upper Case: TEST"), Is.True);

        }

    }

​

     [Test]

    public void CaseConversion_ToLower_PrintsLowerCaseString()

    {

        // Arrange

        using (var consoleOutput = new StringWriter())

        {

            Console.SetOut(consoleOutput);

​

            // Act

            // Simulate user input (string and choice 2)

            string input = "TEST";

            var stringReader = new StringReader(input + Environment.NewLine + "2");

            Console.SetIn(stringReader);

​

            CaseConverter.CaseConversion();

​

            // Assert

            Assert.That(consoleOutput.ToString().Contains("Lower Case: test"), Is.True);

        }

    }

​

    [Test]

    public void CaseConversion_ToToggle_PrintsToggleCaseString()

    {

       // Arrange

        using (var consoleOutput = new StringWriter())

        {

            Console.SetOut(consoleOutput);

​

            // Act

            // Simulate user input (string and choice 3)

            string input = "Test";

            var stringReader = new StringReader(input + Environment.NewLine + "3");

            Console.SetIn(stringReader);

​

            CaseConverter.CaseConversion();

​

            // Assert

            Assert.That(consoleOutput.ToString().Contains("Toggle Case: tEST"), Is.True);

        }

    }

}

​

public class Program 

​

{ 

​

    public static void Main() 

​

    { 

​

        new NUnitLite.AutoRun().Execute(["--noc" /*no colored output for .Net Fiddle*/]); 

​

    } 

​

}