C#单元测试遇System.NotSupportedException：Mock Setup失败求助

运行单元测试时始终抛出System.NotSupportedException异常，问题出在服务Mock的Setup方法上。已知需要进行抽象处理，请问是否需要将一个或多个类声明为abstract或virtual？具体该如何实现？

原代码如下：

public class BaseService
{
    public string GetData(string password)
    {
        string result = "";

        if (password.Equals("password")) 
        {
             result = "granted";
        }

        return result;
    }
}

public class LookupService
{
    private readonly BaseService baseService;

    public LookupService()
    {
        baseService = new BaseService();
    }

    public LookupService(BaseService @base)
    {
        baseService = @base;
    }

    public string GetCode(string password)
    {
        string returnString = baseService.GetData(password);

        return returnString;
    }
}

public class UnitTest_LookupService
{
    LookupService lookupService { get; set; }

    [Fact]
    public void moqTest()
    {
        Mock<BaseService> baseMock = new Mock<BaseService>();

        lookupService = new LookupService(baseMock.Object);

        baseMock.Setup(x => x.GetData("password")).Returns("granted");

        string result = lookupService.GetCode("password");

        Assert.Equal("granted", result);
    }
}

Moq框架仅能Mock虚方法（virtual）、抽象方法（abstract）或接口中的方法——它需要通过生成动态代理类覆盖原有逻辑，普通非虚方法无法被代理，这就是抛出异常的核心原因。

有两种可行的解决方式：

方式一：将目标方法改为virtual #

直接修改BaseService中的GetData方法，添加virtual关键字，让Moq可以生成代理类覆盖该方法：

public class BaseService
{
    // 添加virtual关键字
    public virtual string GetData(string password)
    {
        string result = "";

        if (password.Equals("password")) 
        {
             result = "granted";
        }

        return result;
    }
}

单元测试代码无需修改，即可正常运行。

方式二：使用接口抽象（更推荐） #

遵循依赖倒置原则，面向抽象而非具体实现编程，通过定义接口解耦依赖关系：

1. 定义接口 #

public interface IBaseService
{
    string GetData(string password);
}

2. 修改BaseService实现接口 #

public class BaseService : IBaseService
{
    public string GetData(string password)
    {
        string result = "";

        if (password.Equals("password")) 
        {
             result = "granted";
        }

        return result;
    }
}

3. 修改LookupService依赖接口 #

public class LookupService
{
    private readonly IBaseService _baseService;

    public LookupService()
    {
        _baseService = new BaseService();
    }

    // 构造函数依赖接口而非具体类
    public LookupService(IBaseService baseService)
    {
        _baseService = baseService;
    }

    public string GetCode(string password)
    {
        return _baseService.GetData(password);
    }
}

4. 修改单元测试Mock接口 #

public class UnitTest_LookupService
{
    LookupService lookupService { get; set; }

    [Fact]
    public void moqTest()
    {
        // Mock接口而非具体类
        Mock<IBaseService> baseMock = new Mock<IBaseService>();

        lookupService = new LookupService(baseMock.Object);

        baseMock.Setup(x => x.GetData("password")).Returns("granted");

        string result = lookupService.GetCode("password");

        Assert.Equal("granted", result);
    }
}

这种方式彻底解耦了LookupService与BaseService的具体实现，后续替换BaseService的实现类时无需修改LookupService代码，更符合开闭原则。

内容的提问来源于stack exchange，提问作者user3352070