如何验证在使用 Prism 处理 ViewModel 时调用 EventAggregator 的取消订阅方法

Question

我正在努力编写一个测试，以确认我在 EventAggregator 关闭时正确取消订阅它的消息。有人能指出（简单）答案吗？！

这是代码：

public class ViewModel : BaseViewModel, IViewModel
{
    private readonly IEventAggregator eventAggregator;
    private SubscriptionToken token;
    IssuerSelectedEvent issuerSelectedEvent;

    public ViewModel(IView view, IEventAggregator eventAggregator)
    {
        this.eventAggregator = eventAggregator;
        View = view;        

        issuerSelectedEvent = eventAggregator.GetEvent<IssuerSelectedEvent>();
        token = issuerSelectedEvent.Subscribe(SelectedIssuerChanged, true);            
    }

    private void SelectedIssuerChanged(IssuerSelectedCommand obj)
    {
        Console.WriteLine(obj);
    }

    public IView View { get; set; }

    public override void Dispose()
    {
        issuerSelectedEvent.Unsubscribe(token);
    }
}

测试失败并显示：

Moq.MockVerificationException：以下设置不匹配： IssuerSelectedEvent x =>; x.Unsubscribe(It.IsAny())

这是测试：

[Test]
public void UnsubscribeFromEventAggregatorOnDispose()
{            
    var view = new Mock<ICdsView>();
    var ea = new Mock<EventAggregator>();
    var evnt = new Mock<IssuerSelectedEvent>();

    evnt.Setup(x => x.Unsubscribe(It.IsAny<SubscriptionToken>()));

    var vm = new CdsIssuerScreenViewModel(view.Object, ea.Object);

    vm.Dispose();

    evnt.VerifyAll();
}

Answer 1

在这里，我验证是否在模拟的 IssuerSelectedEvent 上调用了 Unsubscribe

[Test]
public void UnsubscribeFromEventAggregatorOnDispose()
{            
    var view = new Mock<ICdsView>();
    var ea = new Mock<IEventAggregator>();
    var evnt = new Mock<IssuerSelectedEvent>();

    ea.Setup(x => x.GetEvent<IssuerSelectedEvent>()).Returns(evnt.Object);

    var vm = new CdsIssuerScreenViewModel(view.Object, ea.Object);

    vm.Dispose();

    evnt.Verify(x => x.Unsubscribe(It.IsAny<SubscriptionToken>());
}

如果您想检查是否将完全相同的令牌传递到 Unsubscribe 中，则您将需要 Subscribe 方法的 Setup 来返回您在测试中创建的令牌。

Answer 2

您需要告诉您的 EventAggregator 模拟返回您的模拟 IssuerSelectedEvent：

ea.Setup(x => x.GetEvent<IssuerSelectedEvent>()).Return(evnt.Object);

Answer 3

测试需要更改为：

[Test]
public void UnsubscribeFromEventAggregatorOnDispose()
{            
    var view = new Mock<ICdsView>();
    var ea = new Mock<IEventAggregator>();
    var evnt = new Mock<IssuerSelectedEvent>();

    ea.Setup(x => x.GetEvent<IssuerSelectedEvent>()).Returns(evnt.Object);
    evnt.Setup(x => x.Unsubscribe(It.IsAny<SubscriptionToken>()));

    var vm = new CdsIssuerScreenViewModel(view.Object, ea.Object);

    vm.Dispose();

    evnt.VerifyAll();
}