对调用 DispatcherHelper.CheckBeginInvokeOnUI 的异步方法进行单元测试答案

【问题标题】：Unit testing an async method which invokes DispatcherHelper.CheckBeginInvokeOnUI对调用 DispatcherHelper.CheckBeginInvokeOnUI 的异步方法进行单元测试
【发布时间】：2016-10-04 09:07:38
【问题描述】：

我在 Visual Studio 2012 中使用 MVVM Light 5.2。我的单元测试是 MS 测试，我不知道如何测试我的异步方法，因为 DispatcherHelper 不会调用我的操作。使用以下测试，在调试中永远不会到达 Thread.Sleep。

在 MVVM 光源中 DispatcherHelper.CheckBeginInvokeOnUi 调用 UIDispatcher.BeginInvoke(action)，什么都没有发生。我究竟做错了什么？

    [TestMethod]
    public void TestMethod1()
    {
        DispatcherHelper.Initialize();
        TestedMethod();
        // Do assert here
    }

    void TestedMethod()
    {
        ThreadPool.QueueUserWorkItem((o) =>
        {
            // Do stuff
            DispatcherHelper.CheckBeginInvokeOnUI(() =>
            {
                // Do stuff
                Thread.Sleep(1); // Breakpoint here
            });
        });
    }

【问题讨论】：

标签： c# wpf unit-testing mvvm-light

【解决方案1】：

如果它可以提供帮助，因为我不想修改 MVVM 光源，我最后在 DispatcherHelper 上编写了一个代理，它在测试方法中初始化时直接调用操作。它还处理设计模式。

我只需要通过 UIDispatcher 搜索/替换每个 DispatcherHelper，仅此而已。

这里是代码：

public static class UIDispatcher
{
    private static bool _isTestInstance;

    /// <summary>
    ///      Executes an action on the UI thread. If this method is called from the UI
    ///     thread, the action is executed immendiately. If the method is called from
    ///     another thread, the action will be enqueued on the UI thread's dispatcher
    ///     and executed asynchronously.
    ///     For additional operations on the UI thread, you can get a reference to the
    ///     UI thread's dispatcher thanks to the property GalaSoft.MvvmLight.Threading.DispatcherHelper.UIDispatcher
    /// </summary>
    /// <param name="action">The action that will be executed on the UI thread.</param>
    public static void CheckBeginInvokeOnUI(Action action)
    {
        if (action == null)
        {
            return;
        }
        if ((_isTestInstance) || (ViewModelBase.IsInDesignModeStatic))
        {
            action();
        }
        else
        {
            DispatcherHelper.CheckBeginInvokeOnUI(action);
        }
    }

    /// <summary>
    ///     This method should be called once on the UI thread to ensure that the GalaSoft.MvvmLight.Threading.DispatcherHelper.UIDispatcher
    ///     property is initialized.
    ///     In a Silverlight application, call this method in the Application_Startup
    ///     event handler, after the MainPage is constructed.
    ///     In WPF, call this method on the static App() constructor.
    /// </summary>
    /// <param name="isTestInstance"></param>
    public static void Initialize(bool isTestInstance = false)
    {
        _isTestInstance = isTestInstance;
        if (!_isTestInstance)
            DispatcherHelper.Initialize();
    }

    /// <summary>
    ///    Resets the class by deleting the GalaSoft.MvvmLight.Threading.DispatcherHelper.UIDispatcher
    /// </summary>
    public static void Reset()
    {
        if (!_isTestInstance)
            DispatcherHelper.Reset();
    }
}

【讨论】：