使用MOQ模拟嵌套依赖项

Question

我原以为MOQ会自动为所有嵌套依赖项创建模拟对象。

我正在对一个ASP.Net MVC控制器进行单元测试：

public class TransactionController : Controller
{
    private readonly ITransactionService _transactionService;
    private readonly SearchPanelVmBuilder _searchPanelVmBuilder;
    private readonly TransactionVmsBuilder _transactionVmsBuilder;

    public TransactionController(TransactionVmsBuilder transactionVmsBuilder, ITransactionService transactionService, SearchPanelVmBuilder searchPanelVmBuilder)
    {
        _transactionVmsBuilder = transactionVmsBuilder;
        _transactionService = transactionService;
        _searchPanelVmBuilder = searchPanelVmBuilder;
    }

    // other methods omitted for brevity

    public PartialViewResult SearchPanel()
    {
        var vm = _searchPanelVmBuilder.BuildVm();

        return PartialView("_SearchPanel", vm);
    }
}

单元测试代码：

[Fact]
public void SeachPanel_Calls_BuildSearchPanelVm()
{
    // Arrange
    var mockTransService = new Mock<ITransactionService>();
    var mockTransVmsBuilder = new Mock<TransactionVmsBuilder>();
    var mockSearchPanelVmBuilder = new Mock<SearchPanelVmBuilder>();
    var controller = new TransactionController(mockTransVmsBuilder.Object, mockTransService.Object, mockSearchPanelVmBuilder.Object);

    // Act
    controller.SearchPanel();

    // Assert
    mockSearchPanelVmBuilder.Verify(x => x.BuildVm());
}

MOQ 抱怨：

无法实例化代理类：MCIP.Web.UI.ViewModelBuilders.Singular.SearchPanelVmBuilder。 找不到无参数构造函数。

无法实例化代理的类：

public class SearchPanelVmBuilder
{
    private readonly ITransactionTypeService _transactionTypeService;
    private readonly TransactionTypeVmBuilder _transactionTypeVmBuilder;
    private readonly UserProvider _userProvider;

    public SearchPanelVmBuilder(
        UserProvider userProvider,
        ITransactionTypeService transactionTypeService,
        TransactionTypeVmBuilder transactionTypeVmBuilder
        )
    {
        _userProvider = userProvider;
        _transactionTypeService = transactionTypeService;
        _transactionTypeVmBuilder = transactionTypeVmBuilder;
    }

    public virtual SearchPanelVm BuildVm()
    {
        return new SearchPanelVm
        {
            Userlist = _userProvider.GetOperators(),
            TransactionTypes =
                _transactionTypeService.GetAll().Select(x => _transactionTypeVmBuilder.BuildVmFromModel(x)).ToList()
        };
    }
}

对应的依赖项：

public class UserProvider
{
    private static int retryCount;

    public virtual List<string> GetOperators()...

    public virtual List<string> GetGroupsForUser(WindowsIdentity identity)...
}

public interface ITransactionTypeService
{
    List<TransactionType> GetAll();
}

public class TransactionTypeVmBuilder
{
    public virtual TransactionTypeVm BuildVmFromModel(TransactionType transactionType)...
}

我做错了什么吗？

我需要明确告诉MOQ去自动模拟嵌套的依赖关系吗？

还是我必须明确设置嵌套的Mock - 类似于此：

var mockUserProvider = new Mock<UserProvider>();
var mockTransTypeService = new Mock<ITransactionTypeService>();
var mockTransactionTypeVmBuilder = new Mock<TransactionTypeVmBuilder>();
var mockSearchPanelVmBuilder = new Mock<SearchPanelVmBuilder>(mockUserProvider.Object, mockTransTypeService.Object, mockTransactionTypeVmBuilder.Object);

- JTech

---

个人而言，我尽量让我的类依赖于接口而不是具体类，这样我就可以在单元测试中进行大量模拟，并真正限制每个测试的范围。 - ESG

简而言之，拥有接口并不能解决问题。那些没有接口的类具有虚拟方法，它们仍然可以像接口一样被 mock out。由于它们永远不会有替代实现，纯粹为了允许 mocking 而使用接口是不必要的。 - JTech

Answer 1

是的，您的假设是正确的。因为类 SearchPanelVmBuilder 没有提供无参数构造函数，所以无法像这样创建此类的 Mock：

var mockSearchPanelVmBuilder = new Mock<SearchPanelVmBuilder>()

会引发异常：找不到无参数构造函数。

---

相反，通过提供所有参数来创建 Mock，就像这样：

UserProvider userProvider = new UserProvider();
Mock<ITransactionTypeService> transactionTypeService = new Mock<ITransactionTypeService>();
TransactionTypeVmBuilder transactionTypeVmBuilder = new TransactionTypeVmBuilder();

// Use constructor with parameters here because SearchPanelVmBuilder 
// doesn't have parameterless constructor
var mockSearchPanelVmBuilder = new Mock<SearchPanelVmBuilder>(
    userProvider, transactionTypeService.Object, transactionTypeVmBuilder);

var mockTransService = new Mock<ITransactionService>();
var mockTransVmsBuilder = new Mock<TransactionVmsBuilder>();

var controller = new TransactionController(
    mockTransVmsBuilder.Object, 
    mockTransService.Object, 
    mockSearchPanelVmBuilder.Object);

然后可以创建控制器实例TransactionController并调用其方法SearchPanel。

- Daniel Dušek

---

谢谢你的回答！所以Moq真的没有办法自动解决嵌套依赖项，就像StructureMap一样吗？ - JTech

不客气！就我所了解的C#构造函数的工作方式，是没有的。但你可以查看例如这个答案或者这个。 - Daniel Dušek

Answer 2

在这种情况下，您只需要测试是否调用了BuildVM方法并返回了结果，因此不需要模拟内部依赖项。但是，在调用SearchPanel方法之前，您需要在安排部分设置BuildVM方法的返回值。

mockSearchPanelVmBuilder.Setup(x => x.BuildVM()).Returns(mockSearchPanelVM);

如果你在模拟一个类和虚方法时没有设置返回值，实际的实现将会被运行。使用接口将会抛出错误，提示你需要设置返回值。

- chief7