I'm getting into writing unit testing and have implemented a nice repository pattern/moq to allow me to test my functions without using "real" data. So far so good.. However.. In my repository interface for "Posts" IPostRepository I have a function: Post getPostByID(int id); I want to be able to test this from my Test class but cannot work out how. So far I am using this pattern for my tests: [SetUp] public void Setup() { mock = new Mock<IPostRepository>(); } [Test] public void someTest() { populate(10); //This populates the mock with 10 fake entries //do test here } In my function "someTest" I want to be able to call/test the function GetPostById. I can find the function with mock.object.getpostbyid but the "object" is null. Any help would be appreciated :) iPostRepository: public interface IPostRepository { IQueryable<Post> Posts {get;} void SavePost(Post post); Post getPostByID(int id); }