如何纠正异步方法写入测试？ [英] How to correct write test with async methods?

问题描述

我有类迭代的图像。

public class PictureManager
    {
        private int _current;
        public List<BitmapImage> _images = new List<BitmapImage>(5);
        public static string ImagePath = "dataImages";

        public async void LoadImages()
        {
            _images = await GetImagesAsync();
        }
        public async Task<List<BitmapImage>> GetImagesAsync()
        {
            var files = new List<BitmapImage>();
            StorageFolder picturesFolder = await KnownFolders.PicturesLibrary.GetFolderAsync("dataImages");
            IReadOnlyList<IStorageItem> itemsList = await picturesFolder.GetItemsAsync();
            foreach(var item in itemsList)
            {
                if(!(item is StorageFile)) continue;
                var tempImage = new BitmapImage(new Uri(item.Path));
                Debug.WriteLine(string.Format("add {0}", item.Path));
                files.Add(tempImage);
            }
            return files;

        }
}

和我写这篇文章的测试方法（我用NUnit的）：

And I write this test method(I use nUnit):

  [TestFixture]
    public class PictureManagerTest
    {
        private PictureManager _pic;

        [SetUp]
        public void Init()
        {
            _pic = new PictureManager();
            _pic.LoadImages();

        }

        [Test]
        public void ElementOfImagesIsNotNull()
        {
            _pic.GetImagesAsync().ContinueWith(r =>
            {
                BitmapImage image = r.Result[0];
                image = null;
                Assert.IsNotNull(image);
            });
        }
}

为什么这个测试是成功的？

Why this test is successful?

推荐答案

NUnit的，截至目前，不直接支持异步测试（MSTest的和做的xUnit，不过）。

nUnit, as of right now, doesn't directly support asynchronous tests (MSTest and xUnit do, however).

您可以变通的作法是等待的结果，就像这样：

You can work around this by waiting on the results, like so:

    [Test]
    public void ElementOfImagesIsNotNull()
    {
        var continuation = _pic.GetImagesAsync().ContinueWith(r =>
        {
            BitmapImage image = r.Result[0];
            image = null;
            Assert.IsNotNull(image);
        });

        // Block until everything finishes, so the test runner sees this correctly!
        continuation.Wait();
    }

第二个选择，当然是使用像MSTest的，它不支持异步测试code，即：

The second option, of course, would be to use something like MSTest, which does support testing asynchronous code, ie:

    [TestMethod]
    public async Task ElementOfImagesIsNotNull()
    {
        var images = await _pic.GetImagesAsync();

        BitmapImage image = r.Result[0];
        image = null;
        Assert.IsNotNull(image);
    }

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