Curricula recommendation for undergraduate Software Engineering courses underscore the importance of transcending from traditional lecture format to actively involving students in time-limited, iterative development practices. This paper presents a teaching approach for a software testing course that integrates theory and practical experience through the utilization of both TBL and active contributions to OSS projects. The paper reports on our experience implementing the pedagogical approach over four consecutive semesters of a Software Testing course within an undergraduate Software Engineering program. The experience encompassed both online and in-person classes, involving a substantial cohort of over 300 students spanning four semesters. Students' perceptions regarding the course are analyzed and compared with previous, related studies. Our results are positively aligned with the existing literature of software engineering teaching, confirming the effectiveness of combining TBL with OSS contributions. Additionally, our survey has shed light on the challenges that students encounter during their first contribution to OSS projects, highlighting the need for targeted solutions. Overall, the experience demonstrates that the proposed pedagogical structure can effectively facilitate the transition from theoretical knowledge to real-world practice in the domain of Software Testing.