There seems to be a divide in the Rails/TDD community over whether you should bother testing your model validations. On the one hand, it’s silly to just retest what the Rails core team has hopefully already tested — that validations work. On the other hand, I want to make sure that my models only accept the data that I design them to accept. I also tend to use my RSpec unit tests as blueprints for building out my models, in true TDD fashion, so I start out by defining what values they should accept.