design

 

I have repository class that is used by at least 2 other classes. This repository class needs to be initialized - which is high in cost (querying database). Now, I create separate instances of repository wherever I need it. The thing is, that everytime I create repository it has to be initialized. How to design such repository to be TDD-friendly? The first thing in my mind was Singleton but it's not the solution.

Do you use any type of IOC container? Unity is my container of choice, and it contains a ContainerControledLifetimeManager which makes your class a singleton, but not managed by yourself.

I hope by TDD-friendly you mean 'testable' code. For a Singleton ObjectX, I think the most common way is to split the responsibility (SRP) of 'controlling creation' to another class so ObjectX does all the things it is supposed to do.

Then you have another class ObjectXFactory or Host or whatever you wanna call it that is responsible for providing a single instance for all clients (and providing thread sync if needed and so on)

  • Object X can be TDDed independently. You can create a new instance in your test case and test functionality.
  • ObjectXFactory on the other hand is also easy to test.. you just need to see if multiple GetInstance() calls return the same object. OR better delegate this responsibility to an IOC framework like Spring, which lets you declaratively mark an object definition to obtain singleton behavior (Saving you the effort of writing tests as well)

    • You just need to educate and conform to a Team convention that ObjectX constructor is not to be called - always use ObjectXFactory.CreateInstance(). (If you find that you have a awareness/discipline problem, mark ObjectX's ctor as internal and visible to only to the test assembly via the sneaky InternalsVisibleToAttribute) HTH

    One answer for the TDD part is learn mocking.

    Check out this excellent article by Stephen Walther:

    http://stephenwalther.com/blog/archive/2008/03/23/tdd-introduction-to-rhino-mocks.aspx

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