TDD, DDD and Encapsulation

Question

After several years of following the bad practice handed down from \'architects\' at my place of work and thinking that there must be a better way, I\'ve recently been reading u

Answer 1

Hey Justin, like you, I was recently thinking about adding getters to my write-only domain object for the sake of unit testing, but now I am convinced I was wrong. Assuming you've bought into the idea of a write-only domain in the first place, then if you have getters at all, you're asking for trouble. The write-only domain principle would want you to fire an event from your domain object, or read from a projection that your domain object wrote, or something like that. Once you expose getters you're starting to expose the object's "shape", and as Greg Young says, "Domain objects have Behavior, not Shape".

That being said, I am struggling with your same question ... how do you unit test a write-only domain object? Here's my current plan: I am thinking of making my Domain Object fire a Domain Event saying "These properties changed", and in my unit test, I'll register for it before I send the "EditCommand". Check out Udi Dahan's post on Domain Events here, and also see what Eric Evans says about Domain Events.