有什么方法可以模拟结构以在单元测试下获得 class？

Question

我有一个 class 正在尝试进行单元测试。 class 将结构公开为 public 属性。该结构还有一些 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"mock a struct"？

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

通过接口引用结构有效地将其转换为引用类型，在做出决定之前通过称为 "boxing". Boxing a struct can cause some subtle changes in behavior, which you should read about 的过程。

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伪造（Moq，在本例中）...


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漂亮，在将这种后门放入共享库之前，我会认真考虑 safety/security。如果可行，接口通常更可取。

虽然这种方法可行，但我认为当您面对不想侵入式重构的对测试不友好的代码时，这可能是一个公平的折衷方案。

有什么方法可以模拟结构以在单元测试下获得 class？

What are ways to mock out a struct to get a class under unit tests?

c#

tdd

moq

legacy-code