
using Xunit;
using System;
using System.Threading.Tasks;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;

namespace ConsoleApp {
    public class ProgramTests {
        [Fact(DisplayName = "GenerateNumbersAsync yields correct sequence")] 
        public async Task GenerateNumbersAsync_YieldsCorrectSequence() 
        {
            var result = new List<int>();
            await foreach (var n in Program.GenerateNumbersAsync(5, 10))
                result.Add(n);
            Assert.Equal(new List<int> {1,2,3,4,5}, result);
        }

        [Fact(DisplayName = "GenerateNumbersAsync respects delay between items")]
        public async Task GenerateNumbersAsync_RespectsDelay() 
        {
            var sw = Stopwatch.StartNew();
            var count = 3;
            var delay = 100;
            await foreach (var n in Program.GenerateNumbersAsync(count, delay)) { }
            sw.Stop();
            // Total delay should be at least count*delay ms (allowing 80% margin for test speed)
            Assert.True(sw.ElapsedMilliseconds >= count * delay * 0.8, $"Expected at least {count*delay*0.8}ms, got {sw.ElapsedMilliseconds}ms");
        }

        [Fact(DisplayName = "Main consumes async stream with await foreach")]
        public async Task Main_ConsumesAsyncStream() 
        {
            var sw = new System.IO.StringWriter();
            Console.SetOut(sw);
            await Program.TestMain(new string[0]);
            var output = sw.ToString();
            for (int i = 1; i <= 5; i++)
            {
                Assert.Contains($"Received: {i}", output);
            }
            Console.SetOut(new System.IO.StreamWriter(Console.OpenStandardOutput()) { AutoFlush = true });
        }
    }
}

ProgramTests.cs

Master asynchronous programming in C# with hands-on practice and engaging explanations. Learn to convert synchronous code to async, process collections concurrently, handle timeouts, and manage errors effectively using async/await.

Learn the basics of async/await in C# and how to convert synchronous code to asynchronous for better performance and responsiveness.

Explore how to use async/await in loops and process collections of data asynchronously for efficient, scalable code.

Master advanced async/await concepts: handling timeouts, managing sequential vs. parallel tasks, and robust error handling.

Challenge: Implement an Async Stream

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