Comment by axelriet

Integration tests (I think we call them scenario tests in our circles) also only tend to test the happy paths. There is no guarantees that your edge cases and anything unusual such an errors from other tiers are covered. In fact the scenario tests may just be testing mostly the same things as the unit tests but from a different angle. The only way to be sure everything is covered is through fault injection, and/or single-stepping but it’s a lost art. Relying only on automated tests gives a false sense of security.