c# - 有什么方法可以模拟结构以在单元测试下获取类？

Question

我有一个类正在尝试进行单元测试。该类将结构公开为公共(public)属性。该结构还有一些公共(public)方法(比结构中的方法做的更多)。我无法更改结构(我不拥有该代码，目前风险太大)。

Mock 不适用于值类型。有没有办法有效地“模拟结构”？

public class SystemUnderTest
{
    public FragileStructCantChange myStruct {get; set;}

    public string MethodUnderTest()
    {
        if(myStruct.LongRunningMethod() == "successful")
            return "Ok";
        else
            return "Fail";        
    }
}

public struct FragileStructCantChange
{
    public string LongRunningMethod()
    {
        var resultString = DoStuff(); //calls other subsystems            
        return resultString;
    }
}

Answer 1

通过一个称为"boxing" 的过程，通过一个接口(interface)引用一个结构有效地将它变成一个引用类型。 .装箱结构可能会导致行为发生一些细微的变化，您应该这样做 read about在做出决定之前。

另一种选择是在结构和被测代码之间添加一些间接。一种方法是添加一个以指定测试值。

public class SystemUnderTest
{
    public FragileStructCantChange myStruct { get; set; }

    // This value can be overridden for testing purposes
    public string LongRunningMethodOverride { get; set; }

    public string MethodUnderTest()
    {
        // Call the indirect Func instead of referencing the struct directly
        if (LongRunningMethod() == "successful")
            return "Ok";
        else
            return "Fail";
    }

    private string LongRunningMethod()
        => LongRunningMethodOverride ?? myStruct.LongRunningMethod();
}

public class Tests
{

    [Fact]
    public void TestingSideDoor()
    {
        var sut = new SystemUnderTest();

        // Override the func to supply any test data you want
        sut.LongRunningMethodOverride = "successful";

        Assert.Equal("Ok", sut.MethodUnderTest());
    }
}

另一种方法是公开一个可覆盖的函数指针...

public class SystemUnderTest
{
    public FragileStructCantChange myStruct { get; set; }

    // This Func can be overridden for testing purposes
    public Func<string> LongRunningMethod;

    public SystemUnderTest() {
        LongRunningMethod = () => myStruct.LongRunningMethod();
    }

    public string MethodUnderTest()
    {
        // Call the indirect Func instead of referencing the struct directly
        if (LongRunningMethod() == "successful")
            return "Ok";
        else
            return "Fail";
    }
}

public class Tests
{

    [Fact]
    public void TestingSideDoor()
    {
        var sut = new SystemUnderTest();

        // Override the func to supply any test data you want
        sut.LongRunningMethod = () => "successful";

        Assert.Equal("Ok", sut.MethodUnderTest());
    }
}

另一种选择是使用虚方法，它可以由子类或模拟框架(在本例中为 Moq)伪造...

public class SystemUnderTest
{
    public FragileStructCantChange myStruct { get; set; }

    // This method can be overridden for testing purposes
    public virtual string LongRunningMethod()
        => myStruct.LongRunningMethod();

    public string MethodUnderTest()
    {
        // Call the indirect method instead of referencing the struct directly
        if (LongRunningMethod() == "successful")
            return "Ok";
        else
            return "Fail";
    }
}

public class Tests
{

    [Fact]
    public void TestingSideDoor()
    {
        var sut = new Mock<SystemUnderTest>();

        // Override the method to supply any test data you want
        sut.Setup(m => m.LongRunningMethod())
            .Returns("successful");

        Assert.Equal("Ok", sut.Object.MethodUnderTest());
    }
}

我不会说这些选项中的任何一个都很好，在将这种后门放入共享库之前，我会认真考虑安全性。如果可行，接口(interface)通常更可取。

不过，这种方法是可行的，而且我认为当您面对不想进行侵入式重构的测试不友好代码时，这可能是一个公平的折衷方案。