如何模拟持有 CrossFilePicker 的异步方法？

Question

我正在研究 Xamarin.Forms 项目，即使用 Autofac、Moq 和 Plugin.FilePicker。

其中一个按钮命令是调用方法：

private async void OnLoadFileExecute(object obj)
{
    await PickUpFile();
    LoadedPhrases = LoadFromFile(FileLocation);
    PopulateDb(LoadedPhrases);
    LoadGroups();
}

而PickUpFile()方法是async:

public async Task<string> PickUpFile()
{
    try
    {
        FileLocation = "";
        var file = await CrossFilePicker.Current.PickFile();
        if (file != null)
        {
            FileLocation = file.FilePath;
            return FileLocation;
        }
        else
        {
            FileLocation = "";
            return "";
        }
    }
    catch (Exception ex)
    {
        Debug.WriteLine("Exception choosing file: " + ex.ToString());
        return "";
    }
}

我想测试整个命令，所以 OnLoadFileExecute 中的所有方法都将被测试。在那种情况下，我不确定如何将 PickUpFile() 方法设置为 return 一些 string。据我所知，我不能在 interface 中使用异步方法。如果我错了，请纠正我。如果可以，我就可以嘲笑它。

Answer 1

您可以在界面中使用Task。当你模拟它时，你需要 return Task.FromResult

Answer 2

在我看来，它应该是这样的

public interface IFileService {
    Task<string> PickUpFile();
}

public class FileService : IFileService {
    public async Task<string> PickUpFile() {
        // here you have your implementation
    }
}

// Here is the test method
public async Task TestTheService() {
    const string fileName = "filename.txt";

    var fileMocker = new Mock<IFileService>();
    fileMocker.Setup( x => x.PickUpFile() ).Returns( Task.FromResult( fileName ) );
    var mainClass = new MainClass( fileMocker.Object );
    await mainClass.OnLoadFileExecute( null );
    Assert.Equal( fileName, mainClass.FileLocation );
}

// here is the real class

public class MainClass {
    private IFileService FileService { get; }
    public string FileLocation { get; set; }

    public MainClass( IFileService fileService ) {
        FileService = fileService;
    }

    private async Task OnLoadFileExecute( object obj )
    {
        FileLocation = await FileService.PickUpFile();
        LoadedPhrases = LoadFromFile( FileLocation );
        PopulateDb( LoadedPhrases );
        LoadGroups();
    }
}

如何模拟持有 CrossFilePicker 的异步方法？

How can I Mock async method holding CrossFilePicker?

c#

moq

xunit

filepicker