Question

I’m trying to implement a unit test for a function in a project that doesn’t have unit tests and this function requires a System.Web.Caching.Cache object as a parameter. I’ve been trying to create this object by using code such as…

System.Web.Caching.Cache cache = new System.Web.Caching.Cache(); cache.Add(...); 

…and then passing the ‘cache’ in as a parameter but the Add() function is causing a NullReferenceException. My best guess so far is that I can’t create this cache object in a unit test and need to retrieve it from the HttpContext.Current.Cache which I obviously don’t have access to in a unit test.

How do you unit test a function that requires a System.Web.Caching.Cache object as a parameter?

Answer 1

When I’ve been faced with this sort of problem (where the class in question doesn’t implement an interface), I often end up writing a wrapper with associated interface around the class in question. Then I use my wrapper in my code. For unit tests, I hand mock the wrapper and insert my own mock object into it.

Of course, if a mocking framework works, then use it instead. My experience is that all mocking frameworks have some issues with various .NET classes.

public interface ICacheWrapper {    ...methods to support }  public class CacheWrapper : ICacheWrapper {     private System.Web.Caching.Cache cache;     public CacheWrapper( System.Web.Caching.Cache cache )     {         this.cache = cache;     }      ... implement methods using cache ... }  public class MockCacheWrapper : ICacheWrapper {     private MockCache cache;     public MockCacheWrapper( MockCache cache )     {         this.cache = cache;     }      ... implement methods using mock cache... }  public class MockCache {      ... implement ways to set mock values and retrieve them... }  [Test] public void CachingTest() {     ... set up omitted...      ICacheWrapper wrapper = new MockCacheWrapper( new MockCache() );      CacheManager manager = new CacheManager( wrapper );      manager.Insert(item,value);      Assert.AreEqual( value, manager[item] ); } 

Real code

...  CacheManager manager = new CacheManager( new CacheWrapper( HttpContext.Current.Cache ));  manager.Add(item,value);  ...