As an example, when I was first getting to grips with TDD, I was pairing with an experienced agile coach, writing little test methods, then writing the code, and generally feeling good about life. Then I went ahead and wrote some code without a test. When asked why, he answered: "we'll need it in a minute", to which JR, the coach, replied "yes, we might". By using the word "might", he introduced the possibility that we might not. As it turned out, we didn't. - DanNorth
A coach introducing Test-Driven Development to sceptical (i.e. most) developers invariably runs into the same set of objections.
From programmers: Why do I need to write tests? That's what testers do. Writing all these tests slows me down, it's a waste of time. I'm a good programmer! I don't need to write tests to prove my code works And from testers: Why are you getting programmers to write tests? We all know they can't – that's why you need testers. Are you trying to take our jobs away? You obviously don't understand testing or you wouldn't be getting programmers to write tests! This last comment is particularly ironic. In fact, as you will see, the testers take on a central and very important role in Behaviour-Driven Development. An interesting side-effect of BDD is that it reintroduces the role of the Systems Analyst or Architect, something that has been relegated to the sidelines of agile development (“the architecture will sort itself out – let it evolve”), often with dramatic negative consequences. Finally, Behaviour-Driven Development scales. It is equally robust on a programme team of 200 as it is on a project with 4 developers, an analyst and a tester. It leverages techniques developed by ThoughtWorks delivering large (multi-million dollar) programmes of work spanning multiple timezones and three figure team sizes. BDD is not appropriate for all classes of problems. In general the more complex and the more business-critical a software system, the better a fit it will be with BDD. The exceptions to this fit into two categories. The first are pure “number crunching” systems such as financial modelling applications or analytics engines, where there isn't really any incremental benefit until the whole system is in place.These systems are typified by having an exclusively data-oriented test strategy (matching inputs with outputs). The system has no “behaviour” as such, just a beast of a calculation (or other) engine. It is sometimes possible to deliver such a system incrementally, but this is the exception rather than the norm. The other category is a Pure Package System. In this case we are simply bolting together existing third-party packages, so the behaviour-driven model doesn't apply.1 BDD can work with embedded systems development, provided you have a sufficiently complete emulator with an appropriate suite of behaviours (test harness) around it.