假设我们如下代码调用了HttpContext.Current.Cache

public class CacheManager
{public static HttpContext mHttpContext = HttpContext.Current;public void SetCache(string key, T value){mHttpContext.Cache.Insert(key, value, null, DateTime.MaxValue, new TimeSpan(0, 100, 0));}public T GetCache(string key){return (T)mHttpContext.Cache.Get(key);}}

现在我有一个类调用了上面的GetCache<T>

public class LanguageController
{private CacheManager cacheManger = new CacheManager();public string Get_UserLanguage(){string userLanguage=cacheManger.GetCache("userLanguage");if (!string.IsNullOrEmpty(userLanguage)) return userLanguage;return "zh-CN";}
}

我们现在需要测LanguageController的Get_UserLanuage,写如下代码

[TestMethod]
public void Test_Get_UserLanguage()
{CacheManager cacheManger = new CacheManager();cacheManger.SetCache("userLanguage", "en-GB");LanguageController languageController = new LanguageController();Assert.AreEqual(languageController.Get_UserLanguage(), "en-GB");}

运行测试，失败，得到如下消息

System.NullReferenceException: Object reference not set to an instance of an object.

跟踪调试，发现下面方法这句mHttpContext.Cache为空

public void SetCache(string key, T value)
{mHttpContext.Cache.Insert(key, value, null, DateTime.MaxValue, new TimeSpan(0, 100, 0));
}

现在，将测试代码改为如下：

[TestMethod]
public void Test_Get_Language_By_Fake()
{HttpContext.Current = new HttpContext(new HttpRequest(null, "http://10.10.50.127/RGV2/devtest1", null), new HttpResponse(null));CacheManager.mHttpContext = HttpContext.Current;CacheManager cacheManger = new CacheManager();cacheManger.SetCache("userLanguage", "en-GB");LanguageController languageController = new LanguageController();Assert.AreEqual(languageController.Get_UserLanguage(), "en-GB");}

测试通过：

总结，当我们测试的包含HttpContext.Current.Cache代码时：

1. 将HttpContext.Current.Cache 公布为类的静态属性，这样测试时，一个地方改了，全部就改过来了

2. 用下面的代码来给HttpContext.Current赋值

HttpContext.Current = new HttpContext(new HttpRequest(null, "http://10.10.50.127/RGV2/devtest1", null), new HttpResponse(null));CacheManager.mHttpContext = HttpContext.Current;

3. 建议所有调用HttpContext获得值的地方，尽量公布为属性，这样方便测试,比如如下的代码我们就直接赋值了,这个和本文关系不大，只是一个实践而已。

public class ConfigController {private string tempConfigPath;public string mConfigPath{get{if (tempConfigPath == null){tempConfigPath = HttpContext.Current.Server.MapPath(@"~/App_Data/config.xml");}return tempConfigPath;}set{tempConfigPath = value;}}
}

4. 我们也可以使用Mock，但是个人认为上面的方法更简单点。