C++ TDD – Acceptance Test Driven Development Explained

This paper demonstrates that TDD adds 15-35% development time in return for a 40-90% reduction in defect density on otherwise like-for-like projects.

The article refers full paper (pdf) - Nachiappan Nagappan, E. Michael Maximilien, Thirumalesh Bhat, and Laurie Williams. “Realizing quality improvement through test driven development: results and experiences of four industrial teams“. ESE 2008.

_{Abstract Test-driven development (TDD) is a software development practice that has been used sporadically for decades.With this practice, a software engineer cycles minute-by-minute between writing failing unit tests and writing implementation code to pass those tests. Testdriven development has recently re-emerged as a critical enabling practice of agile software development methodologies. However, little empirical evidence supports or refutes the utility of this practice in an industrial context. Case studies were conducted with three development teams at Microsoft and one at IBM that have adopted TDD. The results of the case studies indicate that the pre-release defect density of the four products decreased between 40% and 90% relative to similar projects that did not use the TDD practice. Subjectively, the teams experienced a 15–35% increase in initial development time after adopting TDD.}

_{Full paper also briefly summarizes the relevant empirical studies on TDD and their high level results (section 3 Related Works), including George and Williams 2003, Müller and Hagner (2002), Erdogmus et al. (2005) , Müller and Tichy (2001), Janzen and Seiedian (2006).}

The prerequisites are the "Given" part of the equation. This should preferably access the database directly and create the objects you need. So for your case:

Given user "whatf" exists
And user "whatf" has 3 blog posts
When "whatf" logs in
Then he should be shown a list of all his posts

Now, step user "whatf" exists creates a user in the database (we name the user so that we can have a specific definition of the user behind-the-scenes, such that you don't have to say user exists with admin rights and pink theme and password "s3cret" ... over and over).

Step user "whatf" has 3 blog posts creates three blog posts in the database, against that new user. You can be more or less specific here, if you choose. More specific gives you flexibility, less specific gives you more reusable steps.

Step "whatf" logs in should be the first time you use Selenium, to launch the browser and log the user in.

Then, in the confirmation step, you also use Selenium to check that the user is shown a list of all his posts in the response.

Also note that the difference between TDD and BDD is really dictionary. BDD encourages a more behaviour-driven language for your tests. But those tests can still be unit tests. Or they can be acceptance tests (ATDD).

But the difference between what we call a unit-test framework (eg. xUnit) and what we call a BDD framework (eg. Cucumber) is much bigger. A BDD framework is much more accurately called an acceptance-test framework, if we're to compare it to a unit-test framework. There are also unit-test frameworks that are designed with BDD in mind -- we call them context/specification test frameworks (as opposed to arrange/act/assert).