如何在单元测试中使用 Moq 调用同一类中的另一个方法

Question

您好，我是 Moq 框架的新手，对如何使用它有一些疑问。我会举个例子，希望得到答案。

我有两个类，一个接口和一个实现：

public class Vehicle{
   public string RegistrationNumber {get; set;}
   public long VehicleIdentifier { get; set; }
   public Tyre TyreSpecification { get; set; }
}

public class Tyre {
    public long NumberOfTyres {get; set;}
    public long TyreSize { get; set;}
}

public interface ISelecter {
   Vehicle GetVehicleByRegistrationNumber(string registrationNumber);
   Tyre GetTyreSpecification(long vehicleIdentifier);
}

public class Selecter : ISelecter
{
    public Vehicle GetVehicleByRegistrationNumber(string registrationNumber)
    {
        var vehicle = 'Database will give us the vehicle specification';

        //Then we do things with the vehicle object

        //Get the tyre specification
        vehicle.TyreSpecification = GetTyreSpecification(vehicle.VehicleIdentifier);

        return vehicle;

    }

    public Tyre GetTyreSpecification(long vehicleIdentifier)
    {
         var tyre = 'external manufacture system gets the tyre specification';

         //Then do thing with the tyre before returning the object


         return tyre;
    }
}

我想为这些方法编写两个测试。问题是当我为GetVehicleByRegistrationNumber 编写测试时，我不知道如何模拟对GetTyreSpecification 的方法调用。

测试方法如下：

[TestClass]
public class SelecterTest
{
    [TestMethod]
    public void GetTyreSpecification_test()
    {
        //Arrange
        var tyre = new Tyre { NumberOfTyres = 4, TyreSize = 18 };

        var mockSelecter = new Mock<ISelecter>();
        mockSelecter.SetUp(s=>s.GetTyreSpecification(It.IsAny<long>())).Returns(tyre);

        //Act
        var tyreSpec = mockSelecter.Object.GetTyreSpecification(123456);

        //Assert
        Assert.IsTrue(tyreSpec.NumberOfTyres == 4 && tyreSpec.TyreSize == 18);
    }

    [TestMethod]
    public void GetVehicleByRegistrationNumber_test()
    {
        //Arrange
        var vehicle= new Vehicle { VehicleIdentifier = 123456, RegistrationNumber = ABC123, TyreSpecification = new Tyre { Tyresize = 18, NumberOfTyres = 4 }};

        var mockSelecter = new Mock<ISelecter>();
        mockSelecter.SetUp(s=>s.GetVehicleByRegistrationNumber(It.IsAny<string>     ())).Returns(vehicle);

        //Act
        var vehicle = mockSelecter.Object.GetVehicleByregistrationNumber(123456);

        //Assert
        Assert.IsTrue(vehicle.Registrationnumber == "ABC123";
    }
}

在测试方法GetVehicleByRegistrationNumber_test 中如何模拟对getTyreSpecification 的调用？

Answer 1

专注于模拟被测类使您对实际问题视而不见。

来自被测类中的 cmets...

• '数据库将为我们提供车辆规格'
• '外部制造系统获取轮胎规格'

您实际上公开了两个应该注入到类中的依赖项。

为了解释这个答案，假设这些依赖项看起来像这样。

public interface IDatabase {
    Vehicle GetVehicleByRegistrationNumber(string registrationNumber);
}

public interface IExternalManufactureSystem {
    Tyre GetTyreSpecification(long vehicleIdentifier);
}

这意味着Selecter 需要重构以期望这些依赖项。

public class Selecter : ISelecter {
    private IDatabase database;
    private IExternalManufactureSystem externalManufactureSystem;

    public Selecter(IDatabase database, IExternalManufactureSystem externalManufactureSystem) {
        this.database = database;
        this.externalManufactureSystem = externalManufactureSystem;
    }

    public Vehicle GetVehicleByRegistrationNumber(string registrationNumber) {
        //'Database will give us the vehicle specification'
        var vehicle = database.GetVehicleByRegistrationNumber(registrationNumber);

        //Then we do things with the vehicle object

        //Get the tyre specification
        vehicle.TyreSpecification = GetTyreSpecification(vehicle.VehicleIdentifier);

        return vehicle;
    }

    public Tyre GetTyreSpecification(long vehicleIdentifier) {
        //'external manufacture system gets the tyre specification'
        var tyre = externalManufactureSystem.GetTyreSpecification(vehicleIdentifier);

        //Then do thing with the tyre before returning the object

        return tyre;
    }
}

从那里开始，只需要模拟显式需要的依赖项来测试被测方法的行为。

selecter.GetTyreSpecification 不需要访问数据库，因此没有理由模拟和注入它进行测试。

[TestMethod]
public void GetTyreSpecification_test() {
    //Arrange
    var vehicleIdentifier = 123456;
    var expected = new Tyre { NumberOfTyres = 4, TyreSize = 18 };

    var mockSystem = new Mock<IExternalManufactureSystem>();
    mockSystem.Setup(s => s.GetTyreSpecification(vehicleIdentifier)).Returns(expected);

    var selecter = new Selecter(null, mockSystem.Object);

    //Act
    var actual = selecter.GetTyreSpecification(vehicleIdentifier);

    //Assert
    Assert.AreEqual(expected, actual);
}

selecter.GetVehicleByRegistrationNumber 但是需要能够从其他方法获取轮胎规范，因此该测试需要模拟两个依赖项才能完成。

[TestMethod]
public void GetVehicleByRegistrationNumber_test() {
    //Arrange
    var vehicleIdentifier = 123456;
    var registrationNumber = "ABC123";
    var tyre = new Tyre { TyreSize = 18, NumberOfTyres = 4 };
    var expected = new Vehicle {
        VehicleIdentifier = vehicleIdentifier,
        RegistrationNumber = registrationNumber,
        TyreSpecification = tyre
    };

    var mockSystem = new Mock<IExternalManufactureSystem>();
    mockSystem.Setup(s => s.GetTyreSpecification(vehicleIdentifier)).Returns(tyre);

    var mockDatabase = new Mock<IDatabase>();
    mockDatabase.Setup(s => s.GetVehicleByRegistrationNumber(registrationNumber)).Returns(expected);

    var selecter = new Selecter(mockDatabase.Object, mockSystem.Object);

    //Act
    var actual = selecter.GetVehicleByRegistrationNumber(registrationNumber);

    //Assert
    Assert.IsTrue(actual.RegistrationNumber == registrationNumber);
}    

现在解决这个问题，例如，如果 Selecter 类将 GetVehicleByRegistrationNumber 作为 virtual 方法，

public virtual Tyre GetTyreSpecification(long vehicleIdentifier) {
    //...code removed for brevity.
}

有一种方法可以使用 moq 来存根被测对象并模拟该方法进行测试。这并不总是最好的设计，被认为是一种代码味道。但是，在某些情况下，您最终会遇到这种特殊情况。

[TestMethod]
public void GetVehicleByRegistrationNumber_test2() {
    //Arrange
    var vehicleIdentifier = 123456;
    var registrationNumber = "ABC123";
    var tyre = new Tyre { TyreSize = 18, NumberOfTyres = 4 };
    var expected = new Vehicle {
        VehicleIdentifier = vehicleIdentifier,
        RegistrationNumber = registrationNumber,
        TyreSpecification = tyre
    };        

    var mockDatabase = new Mock<IDatabase>();
    mockDatabase.Setup(s => s.GetVehicleByRegistrationNumber(registrationNumber)).Returns(expected);

    var selecter = new Mock<Selecter>(mockDatabase.Object, null) {
        CallBase = true //So that base methods that are not setup can be called.
    }

    selecter.Setup(s => s.GetTyreSpecification(vehicleIdentifier)).Returns(tyre);

    //Act
    var actual = selecter.Object.GetVehicleByRegistrationNumber(registrationNumber);

    //Assert
    Assert.IsTrue(actual.RegistrationNumber == registrationNumber);
} 

在上面的例子中，当selecter.Object.GetVehicleByRegistrationNumber(registrationNumber)被调用时，被mock包裹的基础Selecter会被调用，然后它又会调用被mock主题上的设置覆盖的mocked GetTyreSpecification测试。

在测试具有依赖于抽象成员的已实现成员的抽象类时，您往往会看到这一点。

Answer 2

您不应该尝试在您要测试的类上模拟方法。模拟框架用于用虚假调用替换对类接受的依赖项的实际调用，以便您可以专注于测试类的行为，而不会被它所具有的外部依赖项分心。

Selecter 类没有引入外部依赖项，因此您不需要模拟任何内容。如果您不需要并测试实际代码本身，我将始终主张不要嘲笑。显然，为了让您的测试保持原子性，您需要模拟对外部依赖项的调用（如果有）。

Answer 3

一般来说，我们将模拟用于在我们将编写单元测试的类中使用的外部依赖项/其他对象/接口调用。因此，当您为其中一个函数编写测试时，该函数在内部调用同一类中的另一个函数，您不必模拟该函数调用。但是在内部函数中，如果您正在调用外部接口，那么您将不得不模拟外部接口实例并编写具有预期结果的单元测试

Answer 4

 var mockSelecter = new Mock<ISelecter>{ CallBase = true };
 mockSelecter.SetUp(s=>s.GetTyreSpecification(It.IsAny<long>())).Returns(tyre);