C# 我不知道我的MVC单元测试代码有什么问题

好了，伙计们，我是MVC的新手，我正试图从教程中学习，我完全按照上面说的做了，但这让我很困惑

测试方法TestProject1.UnitTest1.DisplayCustomer引发异常： System.NullReferenceException:对象引用未设置为对象的实例。 当我尝试运行单元测试时

我从这里开始学习教程

这是我的档案：

显示客户视图

    Customer ID is : <%= Model.Id %>
    Customer ID is : <%= Model.CustomerCode %>
    <% if (Model.Amount >100) {%>
    This is a Previlaged Customer
    <%} else {  %>
    This is a Normal Customer
    <% } %>

客户控制器

public class CustomerController : Controller
{
    //
    // GET: /Customer/

    public ActionResult Index()
    {
        return View();
    }
    public ActionResult FillCustomer()
    {
        return View();
    }
    public ActionResult DisplayCustomer()
    {
        Customer objCustomer = new Customer();
        objCustomer.Id = 10;
        objCustomer.CustomerCode = "Sparkz";
        objCustomer.Amount = 10.55;
        var myview = View(objCustomer);
        return myview;
    }

}

我的单元测试文件（UnitTest1.cs）： 在这里，我尝试了注释的代码和我在下面写的代码，但都不起作用。 它总是在变量customerViewResult/varresult中获取null

[TestClass]
public class UnitTest1
{
   [TestMethod]
    public void DisplayCustomer()
    {
        //CustomerController obj = new CustomerController();
        //var varresult = obj.DisplayCustomer() as ViewResult;
        //Assert.AreEqual("DisplayCustomer", varresult.ViewName);

        CustomerController controller = new CustomerController();

        var customer = new Customer();

        var customerViewActionResult = controller.DisplayCustomer();
        var customerViewViewResult = customerViewActionResult as ViewResult;


        Assert.AreEqual("DisplayCustomer", customerViewViewResult.ViewName);
    }
}

我从这里开始学习教程

在本教程中，

DisplayCustomer

的返回类型是

ViewResult

，而不是

ActionResult

// As stated in the tutorial
public ViewResult DisplayCustomer()
{
    ...
}

---

调试器说什么？

[TestClass]
public class UnitTest1
{
   [TestMethod]
    public void DisplayCustomer()
    {
        //CustomerController obj = new CustomerController();
        //var varresult = obj.DisplayCustomer() as ViewResult;
        //Assert.AreEqual("DisplayCustomer", varresult.ViewName);

        CustomerController controller = new CustomerController();

        var customer = new Customer();

        var customerViewActionResult = controller.DisplayCustomer();
        var customerViewViewResult = customerViewActionResult as ViewResult;


        Assert.AreEqual("DisplayCustomer", customerViewViewResult.ViewName);
    }
}

// As stated in the tutorial
public ViewResult DisplayCustomer()
{
    ...
}