c# - 模拟 ViewModel 以使用 Moq 进行单元测试？

Question

单元测试的新手。我有一个 WPF 客户端应用程序通过 basicHttpbinding 连接到 WCF 服务。一切都很好。我在我的 viewModel 中使用简单的构造函数依赖注入(inject)，传入一个 IServiceChannel，然后我将其称为服务方法，例如:

IMyserviceChannel = MyService;

public MyViewModel(IMyServiceChannel myService)
{
   this.MyService = myService;  
}

Private void GetPerson()
{
  var selectedPerson = MyService.GetSelectedPerson();
}

然后我在客户端应用程序中添加了一个 MS 测试项目，我正在尝试使用 Moq 来模拟我的服务:

  [TestMethod]
    public void GetArticleBody_Test_Valid()
    {
        // Create channel mock
        Mock<IIsesServiceChannel> channelMock = new Mock<IIsesServiceChannel>(MockBehavior.Strict);    

        // setup the mock to expect the Reverse method to be called
        channelMock.Setup(c => c.GetArticleBody(1010000008)).Returns("110,956 bo/d, 1.42 Bcfg/d and 4,900 bc/d. ");

        // create string helper and invoke the Reverse method
        ArticleDataGridViewModel articleDataGridViewModel = new ArticleDataGridViewModel(channelMock.Object);
        string result = channelMock.GetArticleBody(1010000008);
        //Assert.AreEqual("cba", result);

        //verify that the method was called on the mock
        channelMock.Verify(c => c.GetArticleBody(1010000008), Times.Once());
    }

测试失败，出现 System.NullReferenceException。对象引用未设置为对象的实例。 在此处的方法调用处:

 string result = articleDataGridViewModel.IsesService.GetArticleBody(1010000008);

所以我在想这是否是最好的方法，或者我是否更好地以某种方式模拟适用于测试的 viewModel 的孤立部分？

Answer 1

我会抛出 NullReferenceException，因为您使用了 MockBehavior.Strict。文档说:

Causes this mock to always throw an exception for invocations that don't have a corresponding setup.

ArticleDataGridViewModel 的构造函数可能会调用您尚未设置的服务的其他方法。另一个问题是，您正在直接调用模拟方法。相反，您应该调用 View 模型的一个方法，该方法调用此方法。

[TestMethod]
public void GetArticleBody_Test_Valid()
{
    // Create channel mock
    Mock<IIsesServiceChannel> channelMock = new Mock<IIsesServiceChannel>();    

    // setup the mock to expect the Reverse method to be called
    channelMock.Setup(c => c.GetArticleBody(1010000008)).Returns("110,956 bo/d, 1.42 Bcfg/d and 4,900 bc/d. ");

    // create string helper and invoke the Reverse method
    ArticleDataGridViewModel articleDataGridViewModel = new ArticleDataGridViewModel(channelMock.Object);
    string result = articleDataGridViewModel.MethodThatCallsService();
    //Assert.AreEqual("cba", result);

    //verify that the method was called on the mock
    channelMock.Verify(c => c.GetArticleBody(1010000008), Times.Once());
}

除此之外，我认为您的方法没有问题。也许 View 模型违反了单一责任原则并且做了比它应该做的更多的事情，但是根据您的代码示例很难判断。

编辑:这是一个完整的例子，说明如何测试这样的东西:

public interface IMyService
{
    int GetData();
}

public class MyViewModel
{
    private readonly IMyService myService;

    public MyViewModel(IMyService myService)
    {
        if (myService == null)
        {
            throw new ArgumentNullException("myService");
        }

        this.myService = myService;
    }

    public string ShowSomething()
    {
        return "Just a test " + this.myService.GetData();
    }
}

class TestClass
{
    [TestMethod]
    public void TestMethod()
    {
        var serviceMock = new Mock<IMyService>();
        var objectUnderTest = new MyViewModel(serviceMock.Object);

        serviceMock.Setup(x => x.GetData()).Returns(42);

        var result = objectUnderTest.ShowSomething();

        Assert.AreEqual("Just a test 42", result);
        serviceMock.Verify(c => c.GetData(), Times.Once());
    }
}