等待一个异步虚空方法调用的单元测试

问题描述

我有一个看起来像这样的方法：

I have a method that looks like this:

private async void DoStuff(long idToLookUp)
{
    IOrder order = await orderService.LookUpIdAsync(idToLookUp);

    // Close the search
    IsSearchShowing = false;
}

//Other stuff in case you want to see it
public DelegateCommand<long> DoLookupCommand{ get; set; }
ViewModel()
{
     DoLookupCommand= new DelegateCommand<long>(DoStuff);
}

我想进行单元测试这样的：

I am trying to unit test it like this:

[TestMethod]
public void TestDoStuff()
{
    //+ Arrange
    myViewModel.IsSearchShowing = true;

    // container is my Unity container and it setup in the init method.
    container.Resolve<IOrderService>().Returns(orderService);
    orderService = Substitute.For<IOrderService>();
    orderService.LookUpIdAsync(Arg.Any<long>())
                .Returns(new Task<IOrder>(() => null));

    //+ Act
    myViewModel.DoLookupCommand.Execute(0);

    //+ Assert
    myViewModel.IsSearchShowing.Should().BeFalse();
}

，不然我和嘲笑了LookUpIdAsync做我的断言被调用。在我的正常code，这就是我想要的。但是，对于我的单元测试，我不希望出现这种情况。

My assert is called before I get done with the mocked up LookUpIdAsync. In my normal code, that is just what I want. But for my Unit test I don't want that.

我使用的BackgroundWorker转换为异步/等待。随着后台工作，这是正常工作，因为我可以等待BackgroundWorker的完成。

I am converting to Async/Await from using BackgroundWorker. With background worker this was functioning correctly because I could wait for the BackgroundWorker to finish.

但似乎没有成为一个方式来等待一个异步方法无效...

But there does not seem to be a way to wait for a async void method...

如何单元测试这种方法？

推荐答案

我想出了一个办法做到这一点的单元测试：

I figured out a way to do it for unit testing:

[TestMethod]
public void TestDoStuff()
{
    //+ Arrange
    myViewModel.IsSearchShowing = true;

    // container is my Unity container and it setup in the init method.
    container.Resolve<IOrderService>().Returns(orderService);
    orderService = Substitute.For<IOrderService>();

    var lookupTask = Task<IOrder>.Factory.StartNew(() =>
                                  {
                                      return new Order();
                                  });

    orderService.LookUpIdAsync(Arg.Any<long>()).Returns(lookupTask);

    //+ Act
    myViewModel.DoLookupCommand.Execute(0);
    lookupTask.Wait();

    //+ Assert
    myViewModel.IsSearchShowing.Should().BeFalse();
}

这里的关键是，因为我的单元测试，我可以在我想有我的异步调用（我的异步空内）返回任务替代。然后，我只是确保之前，我继续前进的任务已经完成了。

The key here is that because I am unit testing I can substitute in the task I want to have my async call (inside my async void) to return. I then just make sure the task has completed before I move on.

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