Modern programming has proven harder to do that most expected. Long gone are the days of simple programs and simple operations. Recent software is a mess of strongly dependent internal parts with programmers trying to untangle them as best they can. Tests are an integral component of the process of refactoring. Without them, it is simply not possible. Tests therefore serve a higher purpose, having less to do with proving correctness, and much more to do with have test coverage for future code enhancements, deletions, or refactorings.

Behaviour driven development focuses on human collaboration. It bridges the gaps between stakeholders, designers and developers, because in a BDD spec one might include user flow information, as well as tests and documentation all together. Each professional can focus on their own specialization while collaborating on the same piece of information. That ultimately provides much greater insight on the direction and implementation of the product as both technical and non-technical people can contribute. The main advantage of BDD in comparison to TDD or unit-testing after the fact, is that it provides descriptions of `how` software is should behave, instead of internal code information only developers could understand.