Thursday, September 28, 2006

TypeMock - Designing For Testability

A while back I posted on the reasons I thought TypeMock was so useful, namely because I thought decoupling your classes to allow mock instances in wasn't a good way to design. Anyway Roy Osherove now has links to interesting posts on the topic in this blog entry.

I must say I'm still not sold on the idea that designing for test is the right way to decouple your classes in ways that are useful.

Since most of the unit testing is going to be of the domain layer let me explain my views on why TypeMock helps there.

Lets say that I want my domain layer has to call out to infrastructure code. My first thought would be is that really a good idea? If it is then I want to decouple my domain from the infrastructure as much as possible. So in that situation an interface/dependency injection might be the way to go and you might do that during testing.

However I've found that when I want to do real unit testing I'll want to mock quite a few different classes that are depended on and in many cases the depended on classes are also in the domain layer. In those situations interfaces/factories seem overkill, in fact if I put them in I'm just over-complicating things. Thats when I use TypeMock.

Another thing I've realised is that these I only do state based unit testing and have given up on the interaction based unit testing that mocking (and things like TypeMock/NMock) support. I guess I should rethink that.

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