exception_in_one_task_should_not_affect_others

task-experiment.cs

public class Experiment
{
    private readonly ITestOutputHelper _outputHelper;

    public Experiment(ITestOutputHelper outputHelper)
    {
        _outputHelper = outputHelper;
    }

    [Fact]
    public async Task exception_in_one_task_should_not_affect_others()
    {
        var task1 = Fast();
        var task2 = Fast();
        var task3 = Slow();
        var task4 = Fast();
        var task5 = Slow();
        var task6 = Error(200);
        var task7 = Fast();

        var tasks = new[] { task1, task2, task3, task4, task5, task6, task7 };

        try
        {
            await Task.WhenAll(tasks);
        }
        catch (Exception e)
        {
            var now = DateTime.UtcNow.Ticks;
            _outputHelper.WriteLine($"Done at: {now}\nException: {e.Message}");

            var successfullyCompletedTasks = tasks.Where(x => !x.IsFaulted).Where(x => x.GetAwaiter().IsCompleted);
            var completedTaskCount = successfullyCompletedTasks.Count();
            completedTaskCount.Should().Be(tasks.Length - 1, "expecting all non-faulted tasks to complete");

            var tasksCompletedAt = successfullyCompletedTasks.Select(x => x.Result);
            now.Should().BeGreaterThan(tasksCompletedAt.Select(x => x.Ticks).Max(), "completed tasks should be done before the catch started");

            Action shouldThrow = () => tasks.Where(x => x.IsFaulted).Single().GetAwaiter().GetResult();
            shouldThrow.Should().Throw<Exception>("failed task result throws its exception").WithMessage("Error! Error!");
        }
    }

    private async Task<DateTime> Error(int errorInMs = 500)
    {
        await Task.Delay(errorInMs);
        throw new Exception("Error! Error!");
    }

    private async Task<DateTime> Fast(int endInMs = 100)
    {
        await Task.Delay(endInMs);
        return DateTime.UtcNow;
    }

    private async Task<DateTime> Slow(int endInMs = 3000)
    {
        await Task.Delay(endInMs);
        return DateTime.UtcNow;
    }
}