
using Xunit;
using System;
using System.Diagnostics;
using System.Threading.Tasks;

namespace ConsoleApp {
    public class ProgramTests {
        [Fact(DisplayName = "RunParallelOperationsAsync returns all results in correct order")] 
        public async Task RunParallelOperationsAsync_ReturnsCorrectResults() {
            string[] expected = { "API 1 completed", "API 2 completed", "API 3 completed" };
            var result = await Program.RunParallelOperationsAsync();
            Assert.Equal(expected, result);
        }

        [Fact(DisplayName = "RunParallelOperationsAsync starts operations in parallel and waits for all to finish")] 
        public async Task RunParallelOperationsAsync_ParallelAndWaitsForAll() {
            var sw = Stopwatch.StartNew();
            await Program.RunParallelOperationsAsync();
            sw.Stop();
            // Longest delay is 1500ms. If run sequentially, min would be 3000ms.
            // Allowing some overhead, max expected is 1700ms.
            Assert.InRange(sw.ElapsedMilliseconds, 1400, 2000);
        }

        [Fact(DisplayName = "RunParallelOperationsAsync does not return before all tasks complete")] 
        public async Task RunParallelOperationsAsync_WaitsForAllTasks() {
            var task = Program.RunParallelOperationsAsync();
            // Should not be completed immediately
            Assert.False(task.IsCompleted, "The method returned before awaiting all tasks.");
            await task;
            Assert.True(task.IsCompletedSuccessfully, "The method did not complete successfully.");
        }
    }
}

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: Parallel Async Operations

Solution