In test-driven development, we use tests as executable specifications of what is required of the software we create.

For this to work effectively, our tests have to convey the underlying intent. And this requires us to ponder the relationship between a test and a specification.

First of all, what is a specification? Well, in simple terms it's just a rule. A rule that the software must obey. For example, it might be a rule that says that we cannot transfer money...