Agile Specification-Driven Development

We present an agile approach to Specification-Driven Development, which combines features of Test-Driven Development and the plan-based approach of Design-by-Contract. We argue that both tests and contracts are different types of specifications, and both are useful and complementary for building high quality software. We conclude that it is useful for being able to switch between writing tests and writing contracts, and explain how Specification-Driven Development supports this capability.