Not at all sure how anyone following this advice with, say, a Rails app ever upgrades to a newer version of the framework. When the framework APIs change, you

Not at all sure how anyone following this advice with, say, a Rails app ever upgrades to a newer version of the framework. When the framework APIs change, you need something exercising the code just to verify that it interoperates with the new versions. (Yes, apps and frameworks based on a statically type-checked language would catch some of these cases. But not the ones that change behavior of something while leaving the relevant type signatures intact.)