How to mock data access in private methods

Question

I would like to ask how can I use rhino mocks with in the next example:

   Public Class CustomerService 
    {
      Public void Register()
     {
         Action1();
         Action2();
     }

    private action1 ()
     {
       //this is a call to other dll.
       var isExist = _dataComponentService.CheckIfUserExist(userName);
     } 
   private action2()
     {
       //do some more work...
       // Call to dataComponentService. write some data in the database....
     }
    }

this is only an example for the real code I need to update. The current unit tests are making a real call to the database service. I would like to write a unit tests that checks the behavior in the public Register() with out needing to make a real call to the database service.

is it possible to mock a call to other component that is located in private method without needing to re-write the hole service?

thank you in advanced

Ori

Answer 1

You'll need to do some dependency injection to get your mock into your class-under-test (for more information on DI, check out this article by Martin Fowler). First your 'dataComponentService' class will need to implement an interface:

public interface IDataComponentService
{
    boolean CheckIfUserExist(String user);
}

Then you can inject classes that implement that interface into your CustomerService class by adding an appropriate constructor:

public class CustomerService 
{
    private IDataComponentService _dataComponentService

    // This constructor allows you to inject your dependency into the class
    public CustomerService(IDataComponentService dataComponentService)
    {
        _dataComponentService = dataComponentService;
    }

    Public void Register()
    {
        Action1();
        Action2();
    }

    private action1 ()
    {
        //this is a call to other dll.
        var isExist = _dataComponentService.CheckIfUserExist(userName);
    } 

    private action2()
    {
       //do some more work...
       // Call to dataComponentService. write some data in the database....
    }
}

Now, in your test code your tests you can create a mock of an IDataComponentService...

var dataComponentServiceMock = MockRepository.GenerateMock<IDataComponentService>(); 
//add mock's behavior here...

... and pass it into your class-under-test thus...

var objUt = new CustomerService(dataComponentServiceMock);
objUt.Register();
// check method calls to the mock here...