> add system/integration tests. For me this is clearly the way to go. If you add unit tests to a bad designed interface you are only making it more difficult t

> add system/integration tests. For me this is clearly the way to go. If you add unit tests to a bad designed interface you are only making it more difficult to fix. Now you don't only need to change the interface but also the tests increasing your technical debt. System tests are the best cost/value tests. You only add unit testing to stable code that is not going to change often. System tests cover the same code that the unit tests. Its only disadvantage is that - maybe - it will take more time to know what is failing when something fails as they cover a broader amount of code.