c# - 调用命令接口(interface)时异步测试场景失败

Question

我在 Xamarin 项目中测试 ICommand 场景时遇到问题。我已将逻辑提取到下面的演示中。

场景 N1 运行顺利，但我需要场景 N2 才能工作。场景 N2 的问题在于，一旦到达

await Task.Run(() => Task.Delay(1000)); 

它跳回测试方法 Assert，显然 SetSurveyContext(int x) 尚未执行。

最奇怪的是，如果我从应用程序内部的 Xamarin 框架运行此代码，一切正常，可能是因为我以错误的方式执行命令。

这个问题真的很纠结，我尝试了很多方法来运行命令，但都没有奏效。如果有人遇到同样的问题，请帮助。谢谢。

场景 1 - 工作

[Test]
public async Task NewSurvey_SendObjectWithOnlyDate_StaticSurveyResourceIdAndDateSet()
{
        var mvmTest = new TesterPage();
        await mvmTest.NewSurvey();
        Assert.That(mvmTest.setter, Is.EqualTo(3));
}

public partial class TesterPage : ContentPage
{
    public int setter = 0;

    public TesterPage()
    {
        InitializeComponent ();
    }

    public async Task NewSurvey()
    {
        await PostNewSurvey();
    }

    private async Task PostNewSurvey()
    {
        var response = await Another();
        SetSurveyContext(response);
    }

    private async Task<int> Another()
    {
       await Task.Run(() => Task.Delay(1000));
       return 3;
    }

    private void SetSurveyContext(int x)
    {
        setter = x;
    }
}

测试绿色，一切顺利。

场景 N2 - 失败

[Test]
public async Task NewSurvey_SendObjectWithOnlyDate_StaticSurveyResourceIdAndDateSet()
{
        var mvmTest = new TesterPage();
        mvmTest.NewSurveyCommand.Execute(null);
        Assert.That(mvmTest.setter, Is.EqualTo(3));
}

public partial class TesterPage : ContentPage
{
    public int setter = 0;

    public TesterPage ()
    {
        InitializeComponent ();
        NewSurveyCommand = new Command(async () => await NewSurvey());
    }

    public ICommand NewSurveyCommand { get; private set; }

    public async Task NewSurvey()
    {
        await PostNewSurvey();
    }

    private async Task PostNewSurvey()
    {
        var response = await Another();
        SetSurveyContext(response);
    }

    private async Task<int> Another()
    {
       await Task.Run(() => Task.Delay(1000));
       return 3;
    }

    private void SetSurveyContext(int x)
    {
        setter = x;
    }
}

Answer 1

因为我已经在聊天中与@YuriZolotarev 解决了这个问题，这里是我们为遇到它的其他人找到的解决方案:
问题:
当在 TesterPage.Another() 中调用 Task.Run() 时，主线程跳回到测试方法。它会立即执行 Assert.That()，甚至在 SetSurveyContext 将 setter 设置为 3 之前。
解决方案:
我们找到了在 TesterPage 中创建新私有(private)字段的解决方案，该字段应包含在 TesterPage.Another() 中启动的 Task。这个 Task 可以通过反射在测试方法中等待。一切可能看起来像这样:

[Test]
public async Task NewSurvey_SendObjectWithOnlyDate_StaticSurveyResourceIdAndDateSet()
{
    var mvmTest = new TesterPage();
    mvmTest.NewSurveyCommand.Execute(null);
    // Use Reflection to wait for the task
    (GetInstanceField(typeof(TesterPage), mvmTest, "runningTask") as Task).Wait();
    Assert.That(mvmTest.setter, Is.EqualTo(3));
}

// A helper method to simplify Reflection
internal static object GetInstanceField(Type type, object instance, string fieldName)
{
    BindingFlags bindFlags = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic
    | BindingFlags.Static;
    FieldInfo field = type.GetField(fieldName, bindFlags);
    return field.GetValue(instance);
}

public partial class TesterPage : ContentPage
{
    public int setter = 0;
    private Task runningTask; // The field our Task object is saved in

    public TesterPage ()
    {
        InitializeComponent ();
        NewSurveyCommand = new Command(async () => await (runningTask = NewSurvey()));
    }

    public ICommand NewSurveyCommand { get; private set; }

    public async Task NewSurvey()
    {
        await PostNewSurvey();
    }

    private async Task PostNewSurvey()
    {
        var response = await Another();
        SetSurveyContext(response);
    }

    private async Task<int> Another()
    {
        await Task.Run(() => Task.Delay(1000));
        return 3;
    }

    private void SetSurveyContext(int x)
    {
        setter = x;
    }
}