JavaZone 2010 - Test-Driven Development at the System Scale

We present our experience applying "system-test first" test-driven development (TDD) in the development of large systems and systems-of-systems. We try to address integration and system testing as early as possible. The sooner the system is in a deployable state, the easier it is to react to changing business needs because we can deliver new features to users as soon as is deemed necessary. We therefore start by writing tests that build and deploy the system and interact with it from the outside and, to make those tests pass, add code to the system in the classic "unit-test first" TDD style.
Many teams applying TDD start writing unit-tests and leave integration and system testing until late in the project because they find it difficult to write tests that cope with the distributed architecture and concurrent behaviour of their system. We will describe how we address common pitfalls, including unreliable tests, tests that give false positives, slow-running tests and test code that becomes difficult to maintain as the system grows.
We will also describe how writing system tests guides our architectural decisions. Writing unit tests first guides design of the code to be flexibile and maintainable. In a similar way, we have found that writing system tests first guides the architecture to be easier to monitor, manage and support.
Nat Pryce

Nat Pryce

Nat Pryce has worked as a programmer, architect, trainer, and consultant in a variety of industries, including sports reportage, marketing communications, retail, telecoms, and finance. With a Ph.D. from Imperial College London, he has also worked on research projects and does occasional university teaching. An early adopter of Extreme Programming, he has written or contributed to several open source libraries that support Test Driven Development. He was one of the founding organizers of the London XPDay and regularly presents at international conferences. Nat is based in London, UK.
Steve Freeman

Steve Freeman

Steve Freeman is an independent consultant specializing in Agile software development. A founder member of the London Extreme Tuesday Club, he was chair of the first XPDay and is a frequent organizer and presenter at international conferences. Steve has worked in a variety of organizations, from writing shrink-wrap software for IBM, to prototyping for major research laboratories. Steve has a Ph.D. from Cambridge University, and degrees in statistics and music. Steve is based in London, UK.
Steve and Nat Pryce were joint winners of the 2006 Agile Alliance Gordon Pask award, and co-authored "Growing Object Oriented Software, Guided by Tests" (Addison-Wesley)