
using Xunit;
using Xunit;
using System;
using System.Collections.Generic;
using System.IO;

namespace ConsoleApp {
    public class ProgramTests {
        [Fact(DisplayName = "Returns correct letter frequencies for mixed case input")] 
        public void CountLetterFrequencies_ReturnsCorrectFrequencies() 
        {
            var input = "AaBbCcc!1";
            var expected = new Dictionary<char, int> { { 'a', 2 }, { 'b', 2 }, { 'c', 3 } };
            var result = Program.CountLetterFrequencies(input);
            Assert.Equal(expected, result);
        }

        [Fact(DisplayName = "Counts only alphabetic characters and ignores non-letters")]
        public void CountLetterFrequencies_IgnoresNonLetters() 
        {
            var input = "1234!@#$%^&*()_+-=,./<>?";
            var result = Program.CountLetterFrequencies(input);
            Assert.Empty(result);
        }

        [Fact(DisplayName = "Handles empty string by returning empty dictionary")]
        public void CountLetterFrequencies_HandlesEmptyString() 
        {
            var input = "";
            var result = Program.CountLetterFrequencies(input);
            Assert.Empty(result);
        }

        [Fact(DisplayName = "PrintFrequencies displays each letter and its frequency correctly")]
        public void PrintFrequencies_DisplaysCorrectOutput() 
        {
            var frequencies = new Dictionary<char, int> { { 'h', 1 }, { 'e', 1 }, { 'l', 3 }, { 'o', 2 }, { 'w', 1 }, { 'r', 1 }, { 'd', 1 } };
            var sw = new StringWriter();
            Console.SetOut(sw);
            Program.PrintFrequencies(frequencies);
            string output = sw.ToString();
            foreach (var pair in frequencies)
            {
                Assert.Contains($"Letter '{pair.Key}': {pair.Value}", output);
            }
            Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = true });
        }

        [Fact(DisplayName = "Uppercase and lowercase versions of the same letter are counted together")]
        public void CountLetterFrequencies_UppercaseLowercaseTogether()
        {
            var input = "AaAaaA";
            var result = Program.CountLetterFrequencies(input);
            Assert.True(result.ContainsKey('a'), "Should contain 'a'");
            Assert.Equal(6, result['a']);
        }
    }
}

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: Letter Frequency Counter

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