Lacks in quality of test cases (i.e. test smells) are a recognized cause of issues for the maintainability of test suites and production code. The need to avoid and fix test smells is becoming more and more popular in the scientific community, as well as the importance of knowing how to detect and refactor existing test cases. However, these practices are very little considered in academic testing courses, due also to the difficulty of making them attractive to students. This position paper presents an approach for teaching test smells based on gamification. It exploits a tool, TSGame, that provides a serious game where students can familiarize with test smells by practicing with their detection and removal from JUnit test code. TSGame has been implemented as a web-based application that allows a teacher to assign students test smell detection and refactoring tasks that they have to accomplish in game sessions. Upon completion of the tasks they have the possibility to gain rewards. A preliminary version of the tool has been validated in the context of a Software Testing course at Master degree level, with 36 students that showed the tool effectiveness and usefulness for test smell learning.