using Xunit;
using System;
using System.IO;

namespace ConsoleApp.Tests
{
    public class ProgramTests
    {
        [Fact(DisplayName = "CalculateSavings prints correct days and total for 50 daily, 200 target")]
        public void CalculateSavings_PrintsCorrectOutput()
        {
            var sw = new StringWriter();
            Console.SetOut(sw);

            Program.CalculateSavings(50, 200);

            string output = sw.ToString();
            Assert.Contains("It took 4 days to reach the target.", output);
            Assert.Contains("Total saved: 200", output);

            // Restore standard output
            Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = true });
        }

        [Fact(DisplayName = "CalculateSavings works when target is smaller than daily saving")]
        public void CalculateSavings_TargetLessThanDaily()
        {
            var sw = new StringWriter();
            Console.SetOut(sw);

            Program.CalculateSavings(100, 50);

            string output = sw.ToString();
            Assert.Contains("It took 1 days to reach the target.", output);
            Assert.Contains("Total saved: 100", output);

            Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = true });
        }

        [Fact(DisplayName = "CalculateSavings works for exact multiple of daily saving")]
        public void CalculateSavings_ExactMultiple()
        {
            var sw = new StringWriter();
            Console.SetOut(sw);

            Program.CalculateSavings(25, 100);

            string output = sw.ToString();
            Assert.Contains("It took 4 days to reach the target.", output);
            Assert.Contains("Total saved: 100", output);

            Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = true });
        }
    }
}

ProgramTests.cs

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Challenge: do-while Loop

Solution