Unit testing code using LazyCache

To make testing easier and to follow SOLID principles your code should not depend on an instance of CachingService. Instead you should depend upon the interface IAppCache and use a dependency injection container to pass you an instance of CachingService at runtime.

If you want to unit test IAppCache you have three options

• Use a real in memory cache - pass in new LazyCache.CachingService()
• Use the built in mock - new MockCachingService() (See source)
• Use a mocking library like Moq - new Mock()

Example unit test

Say you want to test an API controller that does some caching:

public class DbTimeController : Controller
{
    private readonly IAppCache cache;
    private readonly DbTimeContext dbContext;

    public DbTimeController(DbTimeContext context, IAppCache cache)
    {
        dbContext = context;
        this.cache = cache;
    }

    [HttpGet]
    [Route("api/dbtime")]
    public DbTimeEntity Get()
    {
        var cachedDatabaseTime = cache.GetOrAdd("DbTimeController.Get", () => dbContext.GeDbTime());
        return cachedDatabaseTime;
    }
}

Then you could test it like this (using NUnit as an example)

[Test]
public void Get_ShouldFetchTheTimeFromTheDatabase_WhenNotInTheCache()
{
    DbTimeEntity fakeEntity = new DbTimeEntity("2000-01-01");
    var fakeDatabaseContext = GetMyInMemoryDatabaseFake(fakeEntity);
    DbTimeController controllerUnderTest = new DbTimeController(fakeDatabaseContext, new MockCachingService());

    DbTimeEntity actual = controllerUnderTest.Get();

    Assert.NotNull(actual);
    Assert.AreEqual("2000-01-01", actual.ToString())
}