I try to adopt the approach of using a functional core with an imperative shell (even if the latter is handled in a OO fashion). This way, I can unit test the

I try to adopt the approach of using a functional core with an imperative shell (even if the latter is handled in a OO fashion). This way, I can unit test the functional core without the need to use mocks or stubs, and rely on integration tests to test the imperative shell.