Students struggle to understand why rigorous testing is necessary, often testing with a small number of examples and testing interactively instead of through a framework. Our goal is to encourage students to meaningfully engage in the testing process. We do so by developing a system, Codetierlist, that gamifies the process of testing on a programming assignment in a first-year programming course (CS2). Student tests for a programming assignment are run against both the instructor solution and other student solutions, and students receive feedback, in the form of a tier-based ranking, on how well their solution compares to fellow students within the shared student test suite. We compared the tests and assignment solutions students produced with and without Codetierlist. We also gathered student and instructor feedback on the experience of using the tool and measured student motivation and self-efficacy regarding testing. Students wrote more functionally correct code with Codetierlist, and they wrote significantly more and more precise tests with Codetierlist, even identifying previously unknown bugs in the instructor solution. We did not detect any changes to student self-efficacy, but students reported feeling more positive about testing and more motivated to test with Codetierlist. However, we also detected negative effects from the gamification method selected, as some students whose code was placed in a lower tier felt discouraged and less able to succeed. Additionally, we found that improvements to motivation and efficacy may vary based on a student’s prior experience. We provide the community with a tool, Codetierlist, for motivating students to engage more actively with testing in an assignment setting, and identify positive aspects of providing students with a target to test against. However, we reiterate the need for caution when introducing gamified elements that might be viewed as encouraging competition, as students who receive negative feedback from a comparison may feel unable to improve their situation.
