无法使用Moq在ASP.NET MVC控制器中模拟方法调用

// 假设有一个IFooService接口和一个FooService实现类
public interface IFooService {
    string GetFoo();
}

public class FooService : IFooService {
    public string GetFoo() {
        return "Foo";
    }
}

// 在控制器中注入IFooService
public class FooController : Controller {
    private readonly IFooService _fooService;

    public FooController(IFooService fooService) {
        _fooService = fooService;
    }

    public ActionResult Index() {
        var foo = _fooService.GetFoo();
        return View((object)foo);
    }
}

// 使用Moq模拟IFooService的GetFoo方法
[TestClass]
public class FooControllerTests {
    [TestMethod]
    public void Index_Returns_Foo() {
        // Arrange
        var mockFooService = new Mock<IFooService>();
        mockFooService.Setup(m => m.GetFoo()).Returns("Foo");
        var controller = new FooController(mockFooService.Object);

        // Act
        var result = controller.Index() as ViewResult;

        // Assert
        Assert.IsNotNull(result);
        Assert.AreEqual("Foo", result.ViewData.Model);
    }
}