To me, the morality of what they did is less interesting than the practical ethics of it. The assessment they gamed by accessing the test bank is meant to provide feedback for how well they are acquiring the material. Getting the answers from the test bank means they were more interested in gaming the system for the credential than they were in feedback about where they need to strengthen their understanding. That suggests to me that they're not really interested in the course material, and I wouldn't be interested in working with any of them in any context which used that material. That's an ethical failure. It could be a failure of the course and the educational system, rather than of the students themselves, but it's a problem, no matter who you assign the blame to.