Chapter 13: Using Contract Testing to Verify an API

We've all had to sign a contract before. Maybe it was when you were buying a house, starting a new job, opening a bank account, and so on. There are a number of other reasons that we sign contracts. I have a filing cabinet where I keep important paperwork and I suspect that about half of the documents in there are contracts of some sort. Why do we use contracts so much? What exactly is a contract?

Contracts help simplify the way we do things. I've been talking about formal signed contracts so far, but there are many other kinds of contracts as well. Philosophers will talk about a social contract, for example. At its heart, a contract is just an agreement between two (or more) parties that outlines what they will do. They are so widespread because they make things much more efficient.

Think about it in terms of me buying your house. In broad terms, the way it would usually work is that once we had agreed on a price...