using Xunit;
using System;
using System.IO;
using System.Reflection;

namespace ConsoleApp
{
    public class ProgramTests
    {
        private static string Run(string inputText, string inputSearch)
        {
            var sw = new StringWriter();
            var originalOut = Console.Out;
            Console.SetOut(sw);

            try
            {
                var flags = BindingFlags.Static | BindingFlags.NonPublic | BindingFlags.Public;

                var textField = typeof(Program).GetField("text", flags);
                var searchField = typeof(Program).GetField("search", flags);

                Assert.NotNull(textField);
                Assert.NotNull(searchField);

                textField!.SetValue(null, inputText);
                searchField!.SetValue(null, inputSearch);

                Program.TestMain(Array.Empty<string>());

                return sw.ToString();
            }
            finally
            {
                Console.SetOut(originalOut);
            }
        }

        [Fact(DisplayName = "Counts occurrences case-insensitively and reports first/last index")]
        public void Main_CountsAndFinds_FirstLast_CaseInsensitive()
        {
            string text = "The theme of the event is 'Theatre'. The THEME matters.";
            string search = "the";
        
            string output = Run(text, search);
        
            Assert.Contains("Count: 6", output);
            Assert.Contains("First index: 0", output);
            Assert.Contains("Last index: 41", output);
        }

        [Fact(DisplayName = "Returns 0 and -1 indices when keyword is not found")]
        public void Main_WhenNotFound_ReturnsZeroAndMinusOnes()
        {
            string text = "Programming in C# is fun!";
            string search = "java";

            string output = Run(text, search);

            Assert.Contains("Count: 0", output);
            Assert.Contains("First index: -1", output);
            Assert.Contains("Last index: -1", output);
        }

        [Fact(DisplayName = "Counts non-overlapping occurrences correctly")]
        public void Main_CountsNonOverlapping()
        {
            // "aaaaa" contains "aa" at indices 0 and 2 (non-overlapping) => 2
            string text = "aaaaa";
            string search = "aa";

            string output = Run(text, search);

            Assert.Contains("Count: 2", output);
            Assert.Contains("First index: 0", output);
            Assert.Contains("Last index: 2", output);
        }

        [Fact(DisplayName = "Handles mixed-case search term correctly")]
        public void Main_MixedCaseSearchTerm_Works()
        {
            string text = "The THE the tHe";
            string search = "ThE";

            string output = Run(text, search);

            // Occurrences at indices 0, 4, 8, 12 => 4
            Assert.Contains("Count: 4", output);
            Assert.Contains("First index: 0", output);
            Assert.Contains("Last index: 12", output);
        }
    }
}

ProgramTests.cs

Master the essentials of string manipulation, text parsing, and efficient text processing in C#. This course guides you from the basics of working with strings to advanced text analysis and formatting, using engaging real-world examples and hands-on challenges.

Explore the basics of strings in C#, including creation, concatenation, and essential properties. Practice manipulating and analyzing text with beginner-friendly challenges.

Advance your skills with string formatting, splitting, trimming, and replacing text. Tackle real-world parsing and formatting tasks.

Apply your string skills to analyze text, check for palindromes, perform frequency analysis, and implement basic ciphers.

Challenge: Count Keyword Occurrences

Solution