Integration Test for Hosted Service in .NET Core

Question

I have a QueueTask Hosted service (.NET Core's new background service) that I'd like to test. My queuedHosted service looks like so:

public QueuedHostedService(IServiceProvider serviceProvider, IBackgroundTaskQueue taskQueue, ILoggerFactory loggerFactory)
{
    TaskQueue = taskQueue;
    _logger = loggerFactory.CreateLogger<QueuedHostedService>();
    _serviceProvider = serviceProvider;
}

protected async override Task ExecuteAsync(CancellationToken stoppingToken)
{
    using (var scope = _serviceProvider.CreateScope())
    {
        while (false == stoppingToken.IsCancellationRequested)
        {
            var workItem = await TaskQueue.DequeueAsync(stoppingToken);
            try
            {
                await workItem(scope.ServiceProvider, stoppingToken);
            }
            catch (Exception ex)
            {
                this._logger.LogError(ex, $"Error occurred executing {nameof(workItem)}.");
            }
        }
    }
}

It just reads tasks from the queue and executes them as they come in. I've already verified that the Hosted Service is working in Production. I wrote a test for it like so:

[TestMethod]
public async Task Verify_Hosted_Service_Executes_Task()
{
    IServiceCollection services = new ServiceCollection();
    services.AddSingleton<ILoggerFactory, NullLoggerFactory>();
    services.AddHostedService<QueuedHostedService>();
    services.AddSingleton<IBackgroundTaskQueue, BackgroundTaskQueue>();
    var serviceProvider = services.BuildServiceProvider();

    var backgroundQueue = serviceProvider.GetService<IBackgroundTaskQueue>();

    var isExecuted = false;
    backgroundQueue.QueueBackgroundWorkItem(async (sp, ct) => {
        isExecuted = true;
    });

    await Task.Delay(10000);
    Assert.IsTrue(isExecuted);
}

However, my callback is never hit. How can I get my task to execute on the Background Service?

Edit

I was mimicking the startup, and assumed my background service would just work, but apparently my service is never started.

How is the Hosted Service normally Started from .NET Core?

Hellbent

In regards to "How to start your hosted service?" You should use GenericHost to run your IHostedService. You will also need to configure service dependencies. – Seroka

Answer 1

Hosted services are started by the framework as part of the WebHost's start process

// Fire IHostedService.Start
await _hostedServiceExecutor.StartAsync(cancellationToken).ConfigureAwait(false);

Source

via the HostedServiceExecutor which would take a collection of all the registered IHostedService, enumerate them and start them in turn

public HostedServiceExecutor(ILogger<HostedServiceExecutor> logger, IEnumerable<IHostedService> services)
{
    _logger = logger;
    _services = services;
}

public async Task StartAsync(CancellationToken token)
{
    try
    {
        await ExecuteAsync(service => service.StartAsync(token));
    }
    catch (Exception ex)
    {
        _logger.ApplicationError(LoggerEventIds.HostedServiceStartException, "An error occurred starting the application", ex);
    }
}

Source

But since you are testing the hosted service on its own, you have to act as the framework and start the service yourself.

[TestMethod]
public async Task Verify_Hosted_Service_Executes_Task() {
    IServiceCollection services = new ServiceCollection();
    services.AddSingleton<ILoggerFactory, NullLoggerFactory>();
    services.AddHostedService<QueuedHostedService>();
    services.AddSingleton<IBackgroundTaskQueue, BackgroundTaskQueue>();
    var serviceProvider = services.BuildServiceProvider();

    var service = serviceProvider.GetService<IHostedService>() as QueuedHostedService;

    var backgroundQueue = serviceProvider.GetService<IBackgroundTaskQueue>();

    await service.StartAsync(CancellationToken.None);

    var isExecuted = false;
    backgroundQueue.QueueBackgroundWorkItem(async (sp, ct) => {
        isExecuted = true;
    });

    await Task.Delay(10000);
    Assert.IsTrue(isExecuted);

    await service.StopAsync(CancellationToken.None);
}

Spelter

I had to use var service = serviceProvider.GetService<IHostedService>(); instead of QueuedHostedService to get service to be populated. – Tater

@Tater QueuedHostedService was directly referring to the type they were using in their question. – Spelter

@Spelter When I just used the Type of my class that I also entered in AddHostedService, GetService returned null for me. It wouldn't return the type I entered in AddHostedService until I changed it to be IHostedService. Perhaps I was doing something else different though. – Tater

@Tater then the problem was with my code. Upon further review, the behavior you described is correct as I see no direct registration of that class with the service collection. – Spelter

you can also get the new service with(especially yseful if you have multipleIHostedInstaces registered) serviceProvider.GetServices<IHostedService>().OfType<YourType>().Single(); – Chenoweth

services.AddSingleton<ILoggerFactory, NullLoggerFactory>(); Didn't work for me, I used services.AddLogging(config => config.AddDebug()); – Fiora

In my case the hosted service starts immediately without calling service.StartAsync as it does normally. – Queensland