Sounds good in theory, in practise though in large scale systems you'll need to mock most of the code going to external resources (queus/dependant services/dbs), mocking these eventually requires you to skip rather large parts of code during testing at best this gives you a falae sense of security in your code at worstyou spend all your time maintaining mocks. Integration tests however avoid this problem entirly, they test(if done right) actual User Stories which is what the bussiness really cares about, not if a function was mocked properly.