The central differences between TDD and BDD is evident in the approach to modeling software and web applications. While TDD defines test cases before the software is created to automatically test the functionalities later, behavior-driven development outlines the desired behavior of the software from the point of view of a user, similar to the user stories in extreme programming. These requirements are formulated in a language that facilitates the integration of tasks, objectives, and results of a software in different frameworks and systems, and guides the methodology of software design.
The language is intended to simplify the implementation of the desired behavior of a software by means of certain programming languages so that all involved developers as well as the management can collaborate. Since the definition of test cases can be complex in the case of the test-driven development and difficult for lay persons, the language and the domain-oriented approach with BDD functions as a link between the teams involved and the infrastructure used. At the center of BDD are the vocabulary, framework, methodology, and the objective which the software is to achieve with regard to the user stories.
BDD is characterized by two main features:
A typical example of the behavior-driven design is the formulation of a natural-language scenario, which is directly oriented to the logic of the software. Scenarios are determined using standard logical expressions such as if, then, and, or as well as any given conditions. Each scenario represents an abstract user story that is made possible by the application, such as a login, purchase of a product in an online shop, or the data management of ordered products. The special feature of BDD is the fact that these stories are translated directly into executable tests via ubiquitous language.
An example of a login process on a website:
Depending on the BDD tools and frameworks used, these linguistic sentences are translated into executable code. For this purpose, they are usually arranged in rows from 1 to X and use the vocabulary, which allows the transition of the user story to the technical logic of the program. At the same time, the test cases are adequately specified with the vocabulary, which considerably simplifies the subsequent automated testing of the functionalities of the applications.
Some examples of BDD tools:
Dan North designed behavior-driven software development in response to the complexity of test-driven design. On the one hand, by self-motivation, as he dealt more closely with this important topic within agile methods. On the other hand, he wanted to facilitate access to the advantages of the test-first approach for beginners of agile methods. Against the backdrop of different development environments, TDD led to misunderstandings and conflicts if the testing was not carried out extensively and correctly. The ubiquitous language used with BDD and the focus on user behavior and thus the application is supposed to minimize these misunderstandings and difficulties.
At the same time, project management, quality assurance, and the engineers who set up the infrastructure for development receive important assistance to be able to make the right decisions. Similar to other agile approaches, the workflows, which require a smooth cooperation of the project participants, are at the center of the design. The behavior of the application directs the design process methodically. The ubiquitous language translates this behavior into elements that anticipate an analysis of the code as well as subsequent acceptance tests before the software is finished. The automation of testing can also lead to lower overall costs.