Question

I am refactoring a class so that the code is testable (using NUnit and RhinoMocks as testing and isolations frameworks) and have found that I have found myself with a method is dependent on another (i.e. it depends on something which is created by that other method). Something like the following:

public class Impersonator
{
    private ImpersonationContext _context;

    public void Impersonate()
    {
        ...
        _context = GetContext();
        ...
    }

    public void UndoImpersonation()
    {
        if (_context != null)
            _someDepend.Undo();
    }
}

Which means that to test UndoImpersonation, I need to set it up by calling Impersonate (Impersonate already has several unit tests to verify its behaviour). This smells bad to me but in some sense it makes sense from the point of view of the code that calls into this class:

public void ExerciseClassToTest(Impersonator c)
{
     try
     {
         if (NeedImpersonation())
         {
             c.Impersonate();
         }
         ...
     }
     finally
     {
         c.UndoImpersonation();
     }
}

I wouldn’t have worked this out if I didn’t try to write a unit test for UndoImpersonation and found myself having to set up the test by calling the other public method. So, is this a bad smell and if so how can I work around it?

Answer 1

Code smell has got to be one of the most vague terms I have ever encountered in the programming world. For a group of people that pride themselves on engineering principles, it ranks right up there in terms of unmeasurable rubbish, and about as useless a measure, as LOCs per day for programmer efficiency.

Anyway, that’s my rant, thanks for listening 🙂

To answer your specific question, I don’t believe this is a problem. If you test something that has pre-conditions, you need to ensure the pre-conditions have been set up first for the given test case.

One of the tests should be what happens when you call it without first setting up the pre-conditions – it should either fail gracefully or set up it’s own pre-condition if the caller hasn’t bothered to do so.