BDD, in its essence, is a flavor of TDD. It follows the same basic principle of writing tests (scenarios) before the implementation code. It drives the development and helps to us better understand what should be done.

One of the major differences is the life cycle duration. While with TDD, which is based on unit tests, we're moving from red to green very fast (in minutes if not seconds) BDD often takes a higher-level approach that might require hours or days until we get from the red to the green state. Another important difference is the audience. While unit tests-based TDD is done by developers for developers, BDD intends to involve everyone through its ubiquitous language.

While a whole book can be written on this subject, our intention was to give you just enough information so that you can investigate BDD further.

Now it is time to take a look at legacy code and how to adapt it and make it more TDD friendly.