In this article, we validate the Test-Driven Development Methodology for Internet of Things (IoT)-based Systems (TDDM4IoTS) and its companion tool, called Test-Driven Development Tool for IoT-based Systems (TDDT4IoTS). TDDM4IoTS consists of 11 stages, including activities ranging from system requirements gathering to system maintenance. To evaluate the effectiveness of TDDM4IoTS and TDDT4IoTS, in the last four academic years from 2019, System Engineering students have developed several IoT-based systems as part of their training, from the sixth semester (third academic year). Ñawi (phonetically, Gnawi), which is the case study presented herein, is one of them, and intends to assist visually impaired people to move through open environments. Ñawi consists of a device, a mobile application and a web application. The device interacts with the environment and issues alerts to the user whenever it recognizes obstacles in their path. The mobile application targets two user roles: assisted person and caregiver. Assisted people can use the device and log in into a server when they leave home, so that the mobile application identifies and notifies obstacles in their path. All the collected data is gathered into the server, so that caregivers receive notifications and can monitor the location of their assisted people at any place and time. The web application allows caregivers to query and view more extensive information (details of events, trajectories, etc.). TDDM4IoTS has been evaluated regarding both the roles of the project members and the development cycle stages. A survey was used to evaluate the methodology. Out of a total of 47 respondents, 30 had used TDDM4IoTS and 96.66% of them were very satisfied or satisfied, with nobody unsatisfied
