
using Xunit;
using Xunit;
using System;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Threading.Tasks;

namespace ConsoleApp {
    public class ProgramTests {
        [Fact(DisplayName = "DownloadFileAsync uses Task.Delay for asynchronous delay")]
        public void DownloadFileAsync_UsesTaskDelay()
        {
            var method = typeof(Program).GetMethod("DownloadFileAsync");
            Assert.NotNull(method);
            // Check method body IL for Task.Delay call
            var il = method.GetMethodBody();
            Assert.NotNull(il);
            // Heuristic: check that method is async by checking for AsyncStateMachineAttribute
            Assert.True(method.GetCustomAttributes(typeof(System.Runtime.CompilerServices.AsyncStateMachineAttribute), false).Any(), "Method must be marked async");
        }

        [Fact(DisplayName = "DownloadFileAsync has async signature and returns Task")]
        public void DownloadFileAsync_HasAsyncSignature()
        {
            var method = typeof(Program).GetMethod("DownloadFileAsync");
            Assert.NotNull(method);
            Assert.True(method.ReturnType == typeof(Task), "Method must return Task");
            Assert.True(method.GetCustomAttributes(typeof(System.Runtime.CompilerServices.AsyncStateMachineAttribute), false).Any(), "Method must be marked async");
        }

        [Fact(DisplayName = "MainForTest awaits DownloadFileAsync")]
        public void MainForTest_ExistsAndIsAsync()
        {
            var method = typeof(Program).GetMethod("MainForTest");
            Assert.NotNull(method);
            Assert.True(method.ReturnType == typeof(Task), "MainForTest must return Task");
            Assert.True(method.GetCustomAttributes(typeof(System.Runtime.CompilerServices.AsyncStateMachineAttribute), false).Any(), "MainForTest must be marked async");
        }

        [Fact(DisplayName = "DownloadFileAsync prints 'Download complete!' after delay")]
        public async Task DownloadFileAsync_PrintsDownloadComplete()
        {
            var sw = new StringWriter();
            Console.SetOut(sw);
            await Program.DownloadFileAsync();
            string output = sw.ToString().Trim();
            Assert.Contains("Download complete!", output);
            Console.SetOut(new 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: Convert Synchronous Method to Async

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