Code Defenders is a game that aims to engage students with software testing. Players compete over a Java class under test by producing tests and mutants, i.e., artificial faults, scoring points if tests reveal mutants, or mutants survive tests. While initially created as a fun way to introduce students to testing in one-off fun sessions, we have moved to integrating the game as an assessed core component of a software testing course. This has shown great potential in engaging students, but many challenges have been revealed as part of this integration. In this paper we describe how we integrated Code Defenders into a software testing course, and how we improved the game in order to address the resulting challenges.