c# - 依赖响应 cookie 的集成测试抛出 System.NullReferenceException

Question

我正在尝试找到一种方法来为依赖于 HttpContext 并使用 cookie 的组件编写集成测试。

我的问题是当它试图向响应 cookie 中写入任何内容时抛出异常。

这里有一些重现问题的代码。

using System.IO;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using System.Web;
using Moq;

namespace CookieTest
{
    [TestClass]
    public class CookieTest
    {
        private Mock<HttpContextBase> _httpContextMock;

        [TestInitialize]
        public void SetUp()
        {
            var request = new HttpRequest(null, "http://localhost/", "");
            var stream = new MemoryStream();
            var sw = new StreamWriter(stream);
            var response = new HttpResponse(sw);
            _httpContextMock = new Mock<HttpContextBase>();

            _httpContextMock.Setup(t => t.Request).Returns(new HttpRequestWrapper(request));
            _httpContextMock.Setup(t => t.Response).Returns(new HttpResponseWrapper(response));
        }

        [TestMethod]
        public void TestCookieWrite()
        {
            var httpContext = _httpContextMock.Object;
            var expectedValue = "value";
            var cookies = httpContext.Response.Cookies;
            var cookieToAdd = new HttpCookie("key", expectedValue);

            // to illustrate that these are not null
            Assert.IsNotNull(cookies);
            Assert.IsNotNull(cookieToAdd);

            // System.NullReferenceException: Object reference not set to an instance of an object.
            // at System.Web.HttpCookieCollection.Add(HttpCookie cookie)
            // at CookieTest.CookieTest.TestCookieWrite() in CookieTest.cs: line 41
            cookies.Add(cookieToAdd); 

            Assert.AreEqual(expectedValue, httpContext.Response.Cookies.Get("key"));
        }
    }
}

Answer 1

响应包含一个名为 _context 的私有(private)字段，如果您像这样设置该字段，则它需要对自身和请求的引用:

var response = new HttpResponse(sw);
response.GetType()
        .GetField("_context", BindingFlags.NonPublic | BindingFlags.Instance)
        .SetValue(response, new HttpContext(request, response));
_httpContextMock = new Mock<HttpContextBase>();

然后将不再抛出 NullReferenceException。此外，当您将 HttpCookie 对象与字符串进行比较时，测试失败了，您需要编辑断言以检查 Value 属性，如下所示:

Assert.AreEqual(expectedValue, httpContext.Response.Cookies.Get("key").Value);