c# - ASP.NET MVC Controller 单元测试失败

Question

我尝试测试我的 Controller

[TestMethod]
    public void Index()
    {
        AdminController controller = new AdminController();
        ViewResult result = controller.Index() as ViewResult;
        Assert.IsNotNull(result);
    }

这是Index()代码:

public ActionResult Index()
        {
            var repository = new PostsRepository();
            var posts = repository.GetAllPosts();

            return View(posts);
        }

存储库:

public class PostsRepository : IPostsRepository
    {
        PostsDataContext _dataContext = new PostsDataContext();

        public IQueryable<Post> GetAllPosts()
        {
            var posts = from t in _dataContext.Posts select t;
            return posts;
        }

        public Post GetPostById(int id)
        {
            var post = from t in _dataContext.Posts
                       where t.id == id
                       select t;
            return post.First();
        }
    }

但是我的 Index() 单元测试失败并出现错误:

Test method MvcBlog.Tests.Controllers.AdminControllerTest.Index threw exception: 
System.NullReferenceException: Object reference not set to an instance of an object.

堆栈跟踪:

MvcBlog.Models.PostsDataContext..ctor() in C:\Users\cL1Nk3r\Documents\Visual Studio 2010\Projects\MvcBlog\MvcBlog\Models\Posts.designer.cs: line 38
MvcBlog.Repository.PostsRepository..ctor() in C:\Users\cL1Nk3r\Documents\Visual Studio 2010\Projects\MvcBlog\MvcBlog\Repository\PostsRepository.cs: line 11
MvcBlog.Controllers.AdminController.Index() in C:\Users\cL1Nk3r\Documents\Visual Studio 2010\Projects\MvcBlog\MvcBlog\Controllers\AdminController.cs: line 19
MvcBlog.Tests.Controllers.AdminControllerTest.Index() in C:\Users\cL1Nk3r\Documents\Visual Studio 2010\Projects\MvcBlog\MvcBlog.Tests\Controllers\AdminControllerTest.cs: line 19

为什么会出现错误？
如果我只是运行我的应用程序，它就可以正常工作。

源码下载:http://dl.dropbox.com/u/14053604/MvcBlog.rar

Answer 1

问题出在 Controller 操作中的以下行:

var repository = new PostsRepository();

在这里，您将 Controller 绑定(bind)到存储库的特定实现，这使得单独进行单元测试非常困难。为了在 Controller 和数据访问层之间实现较弱的耦合，我建议您使用构造函数注入(inject):

public class PostsController: Controller
{
    private readonly IPostsRepository _repository;
    public PostsController(IPostsRepository repository)
    {
        _repository = repository;
    }

    public ActionResult Index()
    {
        var posts = _repository.GetAllPosts();
        return View(posts);
    }
}

现在您的 Controller 与存储库的特定实现完全解耦，该存储库可能依赖于数据库等。现在您可以使用模拟框架，例如 Rhino Mocks或Moq为单元测试提供此存储库的虚拟实现。

我个人非常喜欢MVCContrib TestHelper它与 Rhino Mocks 配合使用，并允许对 Controller 操作进行非常优雅的单元测试。因此，一旦您将 Controller 与存储库的特定实现解耦(如我所示)，您就可以进行以下单元测试:

[TestMethod]
public void PostsController_Index_Action_Should_Fetch_All_Posts_From_Repository()
{
    // arrange
    var postsRepositoryStub = MockRepository.GenerateStub<IPostsRepository>();
    var sut = new PostsController(postsRepositoryStub);
    var expectedPosts = new Post[0];
    postsRepositoryStub.Stub(x => x.GetAllPosts).Return(expectedPosts);

    // act
    var actual = sut.Index();

    // assert
    actual
        .AssertViewRendered()
        .WithViewData<IEnumerable<Post>>()
        .ShouldBe(expectedPosts);
}