This work aimed to present part of the implementation of a cellular automaton using Behavior-Driven-Development (BDD) as a strategy for the construction of a tool that allows to model pedestrian accessibility within an open space such as the campus of the Universidad del Valle in Cali, Colombia. For the implementation, BDD was used as a development method, Python as a programming language and Behave to write the tests in natural language. As a result, part of the implemented model of the cellular automaton was presented, some of the requirements with their respective scenarios for BDD and implementation, where the use of the Behave framework in Python was explained. It was concluded that BDD is a good tool for this type of projects because it resulted in 706 lines of source code corresponding to the model of the cellular automatontested with a total of 144 tests defined from the initial phase of the project and successfully passed, a survey of acceptance of the use of the BDD methodology by project users and the first application of BDD in a pedestrian mobility simulation.