Mocking System.Web.Caching.Cache - Layout or check for zero?

Question

I am writing a few unit tests and wondering if it is beneficial to mock Cache , and if so, how?

Currently, in my tests, I mock the HttpContextBase and wrap it in a custom HttpContextFactory :

 var mockedHttpContextBase = new Mock<HttpContextBase>(); IHttpContextFactory httpContextFactory = new HttpContextFactory { Current = mockedHttpContextBase.Object }; 

and when my code consumes an IHttpContextFactory , I check if the cache is zero before doing anything with it.

 var cache = _httpContextFactory.Current.Cache; Func<SomeReturnType> doSomeWork = () => _foo.someMethodIExecute(param1,param2); return cache != null ? cache.GetOrStore("doSomeWorkCacheKey",doSomeWork, 900) : doSomeWork.Invoke(); 

Is it correct to check that the cache is zero, as it is every time I use it, or would you mock the cache also in the test so that it is not zero when performing unit tests?

Answer 1

If your code assumes that the cache can be null and does checks before accessing it (as it is now), you need to have two unit tests for each cache access:

• there is a cache and the element is saved and retrieved (check the GetOrStore call)
• cache is null and you are simply claiming to call a delegate

If this is a common pattern (zero check), instead of two tests every time a cache dependency is required, I suggest wrapping it in a Null Object Pattern and checking it once and later, just use NOP as a dependency that can be mocked.

Edit : example mocking cache

 var cache = new Cache(); // Add takes more parameters; fill whatever is necessary to make it work cache.Add("doSomeWorkCacheKey", doSomeWork, ...); var mockedHttpContextBase = new Mock<HttpContextBase>(); // tell your mock to return pre-configured cache mockedHttpContextBase.Setup(m => m.Cache).Returns(cache); IHttpContextFactory httpContextFactory = new HttpContextFactory { Current = mockedHttpContextBase.Object }; 

Answer 2

After a little searching, it seems that I can use HttpRuntime.Cache instead of System.Web.Caching.Cache when writing unit tests.

Thus:

var mockedHttpContextBase = new Mock<HttpContextBase>(); mockedHttpContextBase.Setup(m => m.Cache).Returns(HttpRuntime.Cache);

The cache should never be null (this would be a suitable exception if it were), so I can remove the null reference check from my code.