对包含HttpContext.Current.Cache的代码进行单元测试

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。